diff --git a/src/backend/api/middleware/api_key.py b/src/backend/api/middleware/api_key.py
index 3f7e5a4..fb48cb3 100644
--- a/src/backend/api/middleware/api_key.py
+++ b/src/backend/api/middleware/api_key.py
@@ -1,10 +1,17 @@
 """API Key authentication dependency for FastAPI."""
+from datetime import timedelta
+
 from fastapi import Depends, HTTPException, Request, status
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from src.backend.database import get_db
+from src.backend.config import settings
+from src.backend.models.orm.api_key import ApiKey
 from src.backend.models.orm.user import User
+from src.backend.services.auth_service import hash_api_key, utcnow
+
+_RENEW_INTERVAL = timedelta(minutes=5)
 
 
 async def get_current_user(
@@ -24,15 +31,25 @@ async def get_current_user(
         )
 
     result = await db.execute(
-        select(User).where(User.api_key == api_key, User.active == True)
+        select(ApiKey, User)
+        .join(User, User.id == ApiKey.user_id)
+        .where(ApiKey.key_hash == hash_api_key(api_key), User.active == True)
     )
-    user = result.scalar_one_or_none()
+    row = result.first()
+    now = utcnow()
 
-    if user is None:
+    if row is None or row[0].expires_at <= now:
         raise HTTPException(
             status_code=status.HTTP_401_UNAUTHORIZED,
-            detail="Invalid or inactive API key",
+            detail="Invalid or expired API key",
         )
+    key_row, user = row
+
+    # Sliding TTL, written at most once per _RENEW_INTERVAL to spare the DB.
+    if key_row.last_used_at is None or now - key_row.last_used_at > _RENEW_INTERVAL:
+        key_row.last_used_at = now
+        key_row.expires_at = now + timedelta(hours=settings.api_key_ttl_hours)
+        await db.flush()
 
     # Store user_id in request state for access logging middleware
     request.state.user_id = user.id
diff --git a/src/backend/api/routers/auth.py b/src/backend/api/routers/auth.py
index bf65c66..4dd8369 100644
--- a/src/backend/api/routers/auth.py
+++ b/src/backend/api/routers/auth.py
@@ -1,5 +1,5 @@
 """Authentication router - login, logout, profile."""
-from fastapi import APIRouter, Depends, HTTPException, status
+from fastapi import APIRouter, Depends, HTTPException, Request, status
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from src.backend.database import get_db
@@ -34,15 +34,16 @@ async def login(data: LoginRequest, db: AsyncSession = Depends(get_db)):
 
 @router.post("/logout", status_code=status.HTTP_204_NO_CONTENT)
 async def logout(
+    request: Request,
     all_sessions: bool = False,
     user: User = Depends(get_current_user),
     db: AsyncSession = Depends(get_db),
 ):
-    """Logout. The API key is shared across stations logged in as the same
-    user, so by default this does not invalidate it - only this station's
-    session (its Flask session, on the client side) ends. Pass
-    ?all_sessions=true to invalidate the key everywhere."""
-    await logout_user(db, user, all_sessions=all_sessions)
+    """Logout. Deletes this session's API key only; ?all_sessions=true
+    deletes every key of the user."""
+    await logout_user(
+        db, user, key=request.headers.get("X-API-Key"), all_sessions=all_sessions
+    )
 
 
 @router.get("/me", response_model=UserResponse)
diff --git a/src/backend/api/routers/setup.py b/src/backend/api/routers/setup.py
index 36ff4d4..5ab3f77 100644
--- a/src/backend/api/routers/setup.py
+++ b/src/backend/api/routers/setup.py
@@ -5,7 +5,6 @@ NOT protected by API Key auth (standalone access).
 """
 import hmac
 import random
-import secrets
 from datetime import datetime, timedelta
 from pathlib import Path
 
@@ -25,7 +24,7 @@ from src.backend.models.orm import (
     User, Recipe, RecipeVersion, RecipeTask, RecipeSubtask, Measurement,
 )
 from src.backend.models.orm.station import Station, StationRecipeAssignment
-from src.backend.services.auth_service import hash_password
+from src.backend.services.auth_service import hash_password, issue_api_key, revoke_all_keys
 from src.backend.services.measurement_service import calculate_pass_fail
 
 router = APIRouter(prefix="/api/setup", tags=["setup"])
@@ -321,8 +320,6 @@ async def create_admin(body: CreateAdminBody):
     """Create an admin user with all roles."""
     _check_password(body.password)
 
-    api_key = secrets.token_hex(32)
-
     async with async_session_factory() as session:
         async with session.begin():
             user = User(
@@ -332,9 +329,10 @@ async def create_admin(body: CreateAdminBody):
                 display_name=body.admin_display_name,
                 roles=["Maker", "MeasurementTec", "Metrologist"],
                 is_admin=True,
-                api_key=api_key,
             )
             session.add(user)
+            await session.flush()
+            api_key = await issue_api_key(session, user)
 
     return {
         "status": "ok",
@@ -404,7 +402,6 @@ async def seed_demo_data(body: PasswordBody):
                     email=u["email"],
                     roles=u["roles"],
                     is_admin=u["is_admin"],
-                    api_key=secrets.token_hex(32),
                 )
                 session.add(user)
                 created_users.append(user)
@@ -652,7 +649,6 @@ async def manage_user(body: ManageUserBody):
                     email=body.email,
                     roles=body.roles,
                     is_admin=body.is_admin,
-                    api_key=secrets.token_hex(32),
                 )
                 session.add(user)
                 await session.flush()
@@ -707,7 +703,7 @@ async def change_user_password(body: ChangeUserPasswordBody):
                     detail=f"User ID {body.user_id} not found",
                 )
             user.password_hash = hash_password(body.new_password)
-            user.api_key = None  # Invalidate sessions
+            await revoke_all_keys(session, user.id)  # Invalidate sessions
 
     return {"status": "ok", "message": f"Password changed for '{user.username}'"}
 
@@ -730,7 +726,7 @@ async def toggle_user_active(body: ToggleUserActiveBody):
                 )
             user.active = not user.active
             if not user.active:
-                user.api_key = None  # Invalidate sessions on deactivation
+                await revoke_all_keys(session, user.id)  # on deactivation
             new_status = "active" if user.active else "inactive"
 
     return {"status": "ok", "message": f"User '{user.username}' is now {new_status}", "active": user.active}
diff --git a/src/backend/api/routers/users.py b/src/backend/api/routers/users.py
index 3abc742..94ae584 100644
--- a/src/backend/api/routers/users.py
+++ b/src/backend/api/routers/users.py
@@ -7,7 +7,7 @@ from src.backend.database import get_db
 from src.backend.api.middleware.api_key import require_admin_user
 from src.backend.models.orm.user import User
 from src.backend.models.api.user import UserCreate, UserPasswordChange, UserResponse, UserUpdate
-from src.backend.services.auth_service import create_user, hash_password, regenerate_api_key
+from src.backend.services.auth_service import create_user, hash_password, regenerate_api_key, revoke_all_keys
 
 router = APIRouter(prefix="/api/users", tags=["users"])
 
@@ -146,7 +146,7 @@ async def change_user_password(
     if user is None:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User not found")
     user.password_hash = hash_password(data.password)
-    user.api_key = None
+    await revoke_all_keys(db, user.id)
     await db.flush()
     return {"message": f"Password changed for user {user.username}"}
 
@@ -168,7 +168,7 @@ async def deactivate_user(
             detail="Cannot deactivate yourself",
         )
     user.active = False
-    user.api_key = None
+    await revoke_all_keys(db, user.id)
     await db.flush()
 
 
@@ -183,5 +183,5 @@ async def regenerate_user_key(
     user = result.scalar_one_or_none()
     if user is None:
         raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="User not found")
-    new_key = await regenerate_api_key(db, user_id)
+    new_key = await regenerate_api_key(db, user)
     return {"api_key": new_key, "message": f"API key regenerated for user {user.username}"}
diff --git a/src/backend/config.py b/src/backend/config.py
index b967388..48ea38a 100644
--- a/src/backend/config.py
+++ b/src/backend/config.py
@@ -38,6 +38,9 @@ class Settings(BaseSettings):
     # configured limits to keep the cluster-wide effective limit close to what
     # was configured instead of multiplying it by N.
     web_concurrency: int = 1
+
+    # API key session lifetime (hours); renewed on use (env API_KEY_TTL_HOURS).
+    api_key_ttl_hours: int = 24
     # How many reverse proxies between the client and this API are trusted to
     # have appended their own hop to X-Forwarded-For (Nginx, in the default
     # deploy). Used by RateLimitMiddleware._client_ip. 0 disables proxy header
diff --git a/src/backend/migrations/versions/015_api_key_hash.py b/src/backend/migrations/versions/015_api_key_hash.py
new file mode 100644
index 0000000..3ea52df
--- /dev/null
+++ b/src/backend/migrations/versions/015_api_key_hash.py
@@ -0,0 +1,54 @@
+"""API keys as SHA-256 hashes, one per session (#41)
+
+Replaces the plaintext `users.api_key` column with an `api_keys` table: one
+row per login, holding only the SHA-256 hex digest, an expiry and the last
+use. Existing keys are invalidated on purpose, not migrated - the plaintext
+is exactly what must stop existing, so everybody logs in once again.
+
+Revision ID: 015_api_key_hash
+Revises: 014_vision_fk_ondelete
+Create Date: 2026-10-06
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = '015_api_key_hash'
+down_revision: Union[str, None] = '014_vision_fk_ondelete'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        'api_keys',
+        sa.Column('id', sa.Integer(), primary_key=True, autoincrement=True),
+        sa.Column('user_id', sa.Integer(), nullable=False),
+        sa.Column('key_hash', sa.String(64), nullable=False),
+        sa.Column('created_at', sa.DateTime(), nullable=False),
+        sa.Column('expires_at', sa.DateTime(), nullable=False),
+        sa.Column('last_used_at', sa.DateTime(), nullable=True),
+        sa.ForeignKeyConstraint(
+            ['user_id'], ['users.id'], name='fk_api_keys_user_id', ondelete='CASCADE'
+        ),
+    )
+    op.create_index('ix_api_keys_key_hash', 'api_keys', ['key_hash'], unique=True)
+    op.create_index('ix_api_keys_user_id', 'api_keys', ['user_id'])
+
+    with op.batch_alter_table('users') as batch:
+        batch.drop_index('ix_users_api_key')
+        batch.drop_constraint('uq_users_api_key', type_='unique')
+        batch.drop_column('api_key')
+
+
+def downgrade() -> None:
+    with op.batch_alter_table('users') as batch:
+        batch.add_column(sa.Column('api_key', sa.String(64), nullable=True))
+        batch.create_unique_constraint('uq_users_api_key', ['api_key'])
+        batch.create_index('ix_users_api_key', ['api_key'])
+
+    op.drop_index('ix_api_keys_user_id', table_name='api_keys')
+    op.drop_index('ix_api_keys_key_hash', table_name='api_keys')
+    op.drop_table('api_keys')
diff --git a/src/backend/models/orm/__init__.py b/src/backend/models/orm/__init__.py
index 361afd1..1afabdb 100644
--- a/src/backend/models/orm/__init__.py
+++ b/src/backend/models/orm/__init__.py
@@ -1,5 +1,6 @@
 """SQLAlchemy models for TieMeasureFlow."""
 from src.backend.models.orm.user import User
+from src.backend.models.orm.api_key import ApiKey
 from src.backend.models.orm.recipe import Recipe, RecipeVersion
 from src.backend.models.orm.task import RecipeTask, RecipeSubtask
 from src.backend.models.orm.measurement import Measurement
@@ -11,6 +12,7 @@ from src.backend.models.orm.vision import VisionReferenceImage, VisionResult
 
 __all__ = [
     "User",
+    "ApiKey",
     "Recipe",
     "RecipeVersion",
     "RecipeTask",
diff --git a/src/backend/models/orm/api_key.py b/src/backend/models/orm/api_key.py
new file mode 100644
index 0000000..8c9fcd5
--- /dev/null
+++ b/src/backend/models/orm/api_key.py
@@ -0,0 +1,25 @@
+"""API key sessions: one row per login, stored as a SHA-256 hash."""
+from datetime import datetime
+from typing import Optional
+
+from sqlalchemy import DateTime, ForeignKey, Integer, String
+from sqlalchemy.orm import Mapped, mapped_column
+
+from src.backend.database import Base
+
+
+class ApiKey(Base):
+    """One API key per login session.
+
+    Only the SHA-256 hex digest is stored, never the key. Dates are naive UTC.
+    """
+    __tablename__ = "api_keys"
+
+    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False, index=True
+    )
+    key_hash: Mapped[str] = mapped_column(String(64), nullable=False, unique=True, index=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime, nullable=False)
+    expires_at: Mapped[datetime] = mapped_column(DateTime, nullable=False)
+    last_used_at: Mapped[Optional[datetime]] = mapped_column(DateTime, nullable=True)
diff --git a/src/backend/models/orm/user.py b/src/backend/models/orm/user.py
index 41c28e0..e5ba358 100644
--- a/src/backend/models/orm/user.py
+++ b/src/backend/models/orm/user.py
@@ -32,7 +32,6 @@ class User(Base):
 
     # Status
     active: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
-    api_key: Mapped[Optional[str]] = mapped_column(String(64), unique=True, nullable=True, index=True)
 
     # Timestamps
     created_at: Mapped[datetime] = mapped_column(
diff --git a/src/backend/services/auth_service.py b/src/backend/services/auth_service.py
index 283a88f..5b2df80 100644
--- a/src/backend/services/auth_service.py
+++ b/src/backend/services/auth_service.py
@@ -1,12 +1,15 @@
 """Authentication service - password hashing, API key management."""
+import hashlib
 import secrets
-from datetime import datetime
+from datetime import datetime, timedelta, timezone
 
 import bcrypt
 from fastapi import HTTPException, status
-from sqlalchemy import select, update
+from sqlalchemy import delete, select, update
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from src.backend.config import settings
+from src.backend.models.orm.api_key import ApiKey
 from src.backend.models.orm.user import User
 
 
@@ -58,8 +61,8 @@ async def authorise_supervisor(db: AsyncSession, username: str, password: str) -
     of them because it is the same question every time - who is this, and are they
     allowed to say yes.
 
-    Uses authenticate_user rather than a full login: logging in would rotate the
-    supervisor's API key and knock out whatever session they have open elsewhere.
+    Uses authenticate_user rather than a full login: logging in would issue a
+    needless API key for the supervisor.
     """
     supervisor = await authenticate_user(db, username, password)
     if supervisor is None:
@@ -75,39 +78,68 @@ async def authorise_supervisor(db: AsyncSession, username: str, password: str) -
     return supervisor
 
 
-async def login_user(db: AsyncSession, user: User) -> str:
-    """Generate (or reuse) the API key and update last_login for user.
+def utcnow() -> datetime:
+    """Naive UTC now (the whole DB moves to naive UTC, #42)."""
+    return datetime.now(timezone.utc).replace(tzinfo=None)
 
-    Reuses an existing key rather than rotating it on every login: the same
-    account logged in from two stations at once (a common shift-account
-    pattern here) must keep both sessions working. Rotating the key would
-    silently log the other station out.
+
+def hash_api_key(key: str) -> str:
+    """SHA-256 hex digest of an API key; this is all the DB ever stores."""
+    return hashlib.sha256(key.encode("utf-8")).hexdigest()
+
+
+async def issue_api_key(db: AsyncSession, user: User) -> str:
+    """Create a new session key for the user and return it in clear (once)."""
+    key = generate_api_key()
+    now = utcnow()
+    db.add(
+        ApiKey(
+            user_id=user.id,
+            key_hash=hash_api_key(key),
+            created_at=now,
+            expires_at=now + timedelta(hours=settings.api_key_ttl_hours),
+            last_used_at=now,
+        )
+    )
+    await db.flush()
+    return key
+
+
+async def revoke_all_keys(db: AsyncSession, user_id: int) -> None:
+    """Invalidate every session key of a user."""
+    await db.execute(delete(ApiKey).where(ApiKey.user_id == user_id))
+    await db.flush()
+
+
+async def login_user(db: AsyncSession, user: User) -> str:
+    """Issue a new API key for this login and update last_login.
+
+    One key per login: the same account used from several stations at once
+    (#25) keeps every station working, because no login revokes another's key.
     """
-    api_key = user.api_key or generate_api_key()
+    api_key = await issue_api_key(db, user)
     await db.execute(
-        update(User)
-        .where(User.id == user.id)
-        .values(api_key=api_key, last_login=datetime.utcnow())
+        update(User).where(User.id == user.id).values(last_login=utcnow())
     )
     await db.flush()
     return api_key
 
 
 async def logout_user(
-    db: AsyncSession, user: User, all_sessions: bool = False
+    db: AsyncSession, user: User, key: str | None = None, all_sessions: bool = False
 ) -> None:
-    """Log out. By default a no-op on the shared API key.
-
-    Clearing the key on every logout would kick out any other station still
-    using the same shift account. `all_sessions=True` is the explicit
-    override for a supervisor who wants every session logged out.
-    """
-    if not all_sessions:
+    """Log out. Deletes only the key of this session; all_sessions=True
+    deletes every key of the user."""
+    if all_sessions:
+        await revoke_all_keys(db, user.id)
         return
-    await db.execute(
-        update(User).where(User.id == user.id).values(api_key=None)
-    )
-    await db.flush()
+    if key:
+        await db.execute(
+            delete(ApiKey).where(
+                ApiKey.user_id == user.id, ApiKey.key_hash == hash_api_key(key)
+            )
+        )
+        await db.flush()
 
 
 async def create_user(
@@ -138,11 +170,7 @@ async def create_user(
     return user
 
 
-async def regenerate_api_key(db: AsyncSession, user_id: int) -> str:
-    """Regenerate API key for a user."""
-    new_key = generate_api_key()
-    await db.execute(
-        update(User).where(User.id == user_id).values(api_key=new_key)
-    )
-    await db.flush()
-    return new_key
+async def regenerate_api_key(db: AsyncSession, user: User) -> str:
+    """Revoke every key of the user and issue a fresh one."""
+    await revoke_all_keys(db, user.id)
+    return await issue_api_key(db, user)
diff --git a/src/backend/tests/conftest.py b/src/backend/tests/conftest.py
index d1a36bb..99092fd 100644
--- a/src/backend/tests/conftest.py
+++ b/src/backend/tests/conftest.py
@@ -40,7 +40,7 @@ from src.backend.models.orm.measurement import Measurement
 from src.backend.models.orm.access_log import AccessLog
 from src.backend.models.orm.setting import SystemSetting, RecipeVersionAudit
 from src.backend.models.orm.station import Station, StationRecipeAssignment
-from src.backend.services.auth_service import hash_password, generate_api_key
+from src.backend.services.auth_service import hash_password, issue_api_key
 
 # ---------------------------------------------------------------------------
 # In-memory SQLite engine for tests
@@ -142,7 +142,6 @@ async def _create_user(
     active: bool = True,
 ) -> User:
     """Insert a user into the test DB and return it with an API key set."""
-    api_key = generate_api_key()
     user = User(
         username=username,
         password_hash=hash_password(password),
@@ -150,13 +149,14 @@ async def _create_user(
         roles=roles or [],
         is_admin=is_admin,
         active=active,
-        api_key=api_key,
         language_pref="en",
         theme_pref="light",
     )
     session.add(user)
     await session.flush()
     await session.refresh(user)
+    # Clear key of this test session; the DB only keeps its hash.
+    user.plain_key = await issue_api_key(session, user)
     return user
 
 
@@ -278,4 +278,4 @@ async def create_test_recipe(
 
 def auth_headers(user: User) -> dict[str, str]:
     """Return headers dict with the user's API key for authenticated requests."""
-    return {"X-API-Key": user.api_key}
+    return {"X-API-Key": user.plain_key}
diff --git a/src/backend/tests/test_auth.py b/src/backend/tests/test_auth.py
index 7a72332..fd0ba54 100644
--- a/src/backend/tests/test_auth.py
+++ b/src/backend/tests/test_auth.py
@@ -78,75 +78,114 @@ class TestLogin:
         assert len(api_key) >= 32
 
 
-class TestLoginKeyReuse:
-    """login_user reuses an existing api_key instead of rotating it (#25)."""
+class TestLoginKeyPerSession:
+    """Each login issues its own key; none revokes another (#25, #41)."""
 
-    async def test_two_logins_same_user_share_api_key(
+    async def test_two_logins_same_user_get_distinct_valid_keys(
         self, client: AsyncClient, db_session
     ):
-        """Two stations logging in as the same shift account both keep working."""
         await _create_user(db_session, username="twostations", password="TwoStations1")
-        resp1 = await client.post(
-            "/api/auth/login",
-            json={"username": "twostations", "password": "TwoStations1"},
-        )
-        resp2 = await client.post(
-            "/api/auth/login",
-            json={"username": "twostations", "password": "TwoStations1"},
-        )
-        assert resp1.status_code == 200
-        assert resp2.status_code == 200
-        assert resp1.json()["api_key"] == resp2.json()["api_key"]
+        creds = {"username": "twostations", "password": "TwoStations1"}
+        resp1 = await client.post("/api/auth/login", json=creds)
+        resp2 = await client.post("/api/auth/login", json=creds)
+        k1, k2 = resp1.json()["api_key"], resp2.json()["api_key"]
+        assert k1 != k2
+        for k in (k1, k2):
+            resp = await client.get("/api/auth/me", headers={"X-API-Key": k})
+            assert resp.status_code == 200
 
-    async def test_login_generates_key_when_user_has_none(
+    async def test_db_stores_hash_never_clear_key(
         self, client: AsyncClient, db_session
     ):
-        """A user created without an api_key (e.g. via create_user) still gets one."""
-        from src.backend.services.auth_service import create_user
+        from sqlalchemy import select
+        from src.backend.models.orm.api_key import ApiKey
+        from src.backend.services.auth_service import hash_api_key
 
-        await create_user(
-            db_session, username="brandnew", password="BrandNew1",
-            display_name="Brand New",
-        )
+        await _create_user(db_session, username="hashed", password="HashedPass1")
         resp = await client.post(
-            "/api/auth/login",
-            json={"username": "brandnew", "password": "BrandNew1"},
+            "/api/auth/login", json={"username": "hashed", "password": "HashedPass1"}
         )
+        key = resp.json()["api_key"]
+        hashes = (await db_session.execute(select(ApiKey.key_hash))).scalars().all()
+        assert hash_api_key(key) in hashes
+        assert key not in hashes
+        assert all(len(h) == 64 for h in hashes)
+
+    async def test_expired_key_gives_401(self, client: AsyncClient, db_session):
+        from datetime import timedelta
+        from sqlalchemy import update
+        from src.backend.models.orm.api_key import ApiKey
+        from src.backend.services.auth_service import utcnow
+
+        user = await _create_user(db_session, username="expired", password="ExpiredPass1")
+        await db_session.execute(
+            update(ApiKey).values(expires_at=utcnow() - timedelta(minutes=1))
+        )
+        resp = await client.get("/api/auth/me", headers=auth_headers(user))
+        assert resp.status_code == 401
+        assert "expired" in resp.json()["detail"].lower()
+
+    async def test_use_renews_expiry_only_after_interval(
+        self, client: AsyncClient, db_session
+    ):
+        from datetime import timedelta
+        from sqlalchemy import select, update
+        from src.backend.models.orm.api_key import ApiKey
+        from src.backend.services.auth_service import utcnow
+
+        user = await _create_user(db_session, username="renew", password="RenewPass1")
+        headers = auth_headers(user)
+        old = utcnow() - timedelta(hours=10)
+
+        # Recent use: no write, expiry untouched.
+        recent = utcnow() - timedelta(minutes=1)
+        await db_session.execute(
+            update(ApiKey).values(expires_at=old + timedelta(hours=24), last_used_at=recent)
+        )
+        await client.get("/api/auth/me", headers=headers)
+        row = (await db_session.execute(select(ApiKey))).scalar_one()
+        await db_session.refresh(row)
+        assert row.last_used_at == recent
+
+        # Stale last use: expiry is pushed forward.
+        await db_session.execute(
+            update(ApiKey).values(last_used_at=utcnow() - timedelta(minutes=10))
+        )
+        before = utcnow()
+        resp = await client.get("/api/auth/me", headers=headers)
         assert resp.status_code == 200
-        assert resp.json()["api_key"]
+        await db_session.refresh(row)
+        assert row.expires_at >= before + timedelta(hours=23, minutes=59)
 
 
 class TestLogout:
-    """POST /api/auth/logout is a no-op on the shared api_key by default (#25)."""
+    """Logout deletes only this session's key (#41)."""
 
-    async def test_logout_default_keeps_api_key_valid(
-        self, client: AsyncClient, db_session
-    ):
-        user = await _create_user(
-            db_session, username="shared_logout", password="SharedPass1"
-        )
-        headers = auth_headers(user)
-        resp = await client.post("/api/auth/logout", headers=headers)
+    async def test_logout_removes_only_own_key(self, client: AsyncClient, db_session):
+        await _create_user(db_session, username="shared_logout", password="SharedPass1")
+        creds = {"username": "shared_logout", "password": "SharedPass1"}
+        k1 = (await client.post("/api/auth/login", json=creds)).json()["api_key"]
+        k2 = (await client.post("/api/auth/login", json=creds)).json()["api_key"]
+        resp = await client.post("/api/auth/logout", headers={"X-API-Key": k1})
         assert resp.status_code == 204
 
-        # The key is still valid: another station on the same account keeps working.
-        resp = await client.get("/api/auth/me", headers=headers)
-        assert resp.status_code == 200
+        assert (await client.get("/api/auth/me", headers={"X-API-Key": k1})).status_code == 401
+        assert (await client.get("/api/auth/me", headers={"X-API-Key": k2})).status_code == 200
 
-    async def test_logout_all_sessions_invalidates_api_key(
+    async def test_logout_all_sessions_removes_every_key(
         self, client: AsyncClient, db_session
     ):
-        user = await _create_user(
-            db_session, username="shared_logout_all", password="SharedPass1"
-        )
-        headers = auth_headers(user)
+        await _create_user(db_session, username="shared_logout_all", password="SharedPass1")
+        creds = {"username": "shared_logout_all", "password": "SharedPass1"}
+        k1 = (await client.post("/api/auth/login", json=creds)).json()["api_key"]
+        k2 = (await client.post("/api/auth/login", json=creds)).json()["api_key"]
         resp = await client.post(
-            "/api/auth/logout", params={"all_sessions": "true"}, headers=headers
+            "/api/auth/logout", params={"all_sessions": "true"},
+            headers={"X-API-Key": k1},
         )
         assert resp.status_code == 204
-
-        resp = await client.get("/api/auth/me", headers=headers)
-        assert resp.status_code == 401
+        for k in (k1, k2):
+            assert (await client.get("/api/auth/me", headers={"X-API-Key": k})).status_code == 401
 
 
 class TestAuthenticateUserTiming:
@@ -185,3 +224,48 @@ class TestHealthAndAuth:
         resp = await client.get("/api/users")
         assert resp.status_code == 401
         assert "API key" in resp.json()["detail"] or "Missing" in resp.json()["detail"]
+
+
+class TestRevokeAllKeys:
+    """Password change, deactivation and regenerate invalidate every key (#41)."""
+
+    async def _two_keys(self, client, db_session, name):
+        user = await _create_user(db_session, username=name, password="KeysPass123")
+        creds = {"username": name, "password": "KeysPass123"}
+        keys = [
+            (await client.post("/api/auth/login", json=creds)).json()["api_key"]
+            for _ in range(2)
+        ]
+        return user, keys
+
+    async def _all_401(self, client, keys):
+        for k in keys:
+            resp = await client.get("/api/auth/me", headers={"X-API-Key": k})
+            assert resp.status_code == 401
+
+    async def test_password_change_invalidates_all(self, client, db_session, admin_user):
+        user, keys = await self._two_keys(client, db_session, "pwkeys")
+        resp = await client.put(
+            f"/api/users/{user.id}/password",
+            headers=auth_headers(admin_user), json={"password": "NewSecurePass1"},
+        )
+        assert resp.status_code == 200
+        await self._all_401(client, keys)
+
+    async def test_deactivation_invalidates_all(self, client, db_session, admin_user):
+        user, keys = await self._two_keys(client, db_session, "offkeys")
+        resp = await client.delete(
+            f"/api/users/{user.id}", headers=auth_headers(admin_user)
+        )
+        assert resp.status_code == 204
+        await self._all_401(client, keys)
+
+    async def test_regenerate_invalidates_old_keys(self, client, db_session, admin_user):
+        user, keys = await self._two_keys(client, db_session, "regenkeys")
+        resp = await client.post(
+            f"/api/users/{user.id}/regenerate-key", headers=auth_headers(admin_user)
+        )
+        assert resp.status_code == 200
+        await self._all_401(client, keys)
+        new = resp.json()["api_key"]
+        assert (await client.get("/api/auth/me", headers={"X-API-Key": new})).status_code == 200
diff --git a/src/backend/tests/test_migrations.py b/src/backend/tests/test_migrations.py
index 4df78a3..9b61d71 100644
--- a/src/backend/tests/test_migrations.py
+++ b/src/backend/tests/test_migrations.py
@@ -107,3 +107,27 @@ class TestBaseMigrationNoopsOnExistingSchema:
         assert "image_path" in {
             c["name"] for c in insp.get_columns("recipes")
         }
+
+
+class TestApiKeyHashMigration:
+    """015_api_key_hash: users.api_key -> api_keys table, and back (#41)."""
+
+    def test_015_upgrade_and_downgrade(self, sqlite_database_url):
+        db_path, _ = sqlite_database_url
+        cfg = _alembic_config()
+        command.upgrade(cfg, "head")
+
+        insp = _inspect(db_path)
+        assert "api_keys" in insp.get_table_names()
+        assert "api_key" not in {c["name"] for c in insp.get_columns("users")}
+        assert {c["name"] for c in insp.get_columns("api_keys")} >= {
+            "user_id", "key_hash", "created_at", "expires_at", "last_used_at",
+        }
+
+        command.downgrade(cfg, "014_vision_fk_ondelete")
+        insp = _inspect(db_path)
+        assert "api_keys" not in insp.get_table_names()
+        assert "api_key" in {c["name"] for c in insp.get_columns("users")}
+
+        command.upgrade(cfg, "head")  # and up again
+        assert "api_keys" in _inspect(db_path).get_table_names()
diff --git a/src/backend/tests/test_user_password_endpoint.py b/src/backend/tests/test_user_password_endpoint.py
index a0ff744..2bf09d7 100644
--- a/src/backend/tests/test_user_password_endpoint.py
+++ b/src/backend/tests/test_user_password_endpoint.py
@@ -17,7 +17,7 @@ class TestChangeUserPassword:
 
         the same as setup.py's change-user-password (setup.py:634).
         """
-        old_key = maker_user.api_key
+        old_key = maker_user.plain_key
         old_username = maker_user.username
         assert old_key is not None
 
@@ -31,7 +31,7 @@ class TestChangeUserPassword:
 
         # The old key no longer authenticates. Read it before the request
         # above: the client and app share one session (see conftest), so
-        # `maker_user.api_key` in this process reflects the mutation too.
+        # `maker_user.plain_key` in this process reflects the mutation too.
         resp2 = await client.get("/api/auth/me", headers={"X-API-Key": old_key})
         assert resp2.status_code == 401