diff --git a/backend/main.py b/backend/main.py
index c5e18fe..59b2d49 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -17,7 +17,7 @@ STATIC_CACHE = f"public, max-age={STATIC_MAX_AGE_SECONDS}, must-revalidate"
 sys.path.insert(0, str(Path(__file__).parent))
 
 from database import Base, engine
-from routers import auth_router, caldav_router, dav_router, google_router, groups_router, homeassistant_router, ical_router, local_router, profile_router, settings_router, users_router
+from routers import auth_router, birthdays_router, caldav_router, dav_router, google_router, groups_router, homeassistant_router, ical_router, local_router, profile_router, settings_router, users_router
 
 logging.basicConfig(level=logging.INFO)
 
@@ -325,6 +325,7 @@ app.include_router(caldav_router.router, prefix="/api/caldav", tags=["caldav"])
 app.include_router(settings_router.router, prefix="/api/settings", tags=["settings"])
 app.include_router(profile_router.router, prefix="/api/profile", tags=["profile"])
 app.include_router(local_router.router, prefix="/api/local", tags=["local"])
+app.include_router(birthdays_router.router, prefix="/api/birthdays", tags=["birthdays"])
 app.include_router(groups_router.router, prefix="/api/groups", tags=["groups"])
 app.include_router(ical_router.router, prefix="/api/ical", tags=["ical"])
 app.include_router(google_router.router, prefix="/api/google", tags=["google"])
diff --git a/backend/models.py b/backend/models.py
index 41cd8bf..483cdff 100644
--- a/backend/models.py
+++ b/backend/models.py
@@ -375,6 +375,26 @@ class GroupMember(Base):
     user = relationship("User")
 
 
+class BirthdaySyncDevice(Base):
+    """A device that has synced Contacts birthdays into the user's birthday
+    calendar. Powers the web "birthdays come from these devices" list. One row
+    per (user, device); the client sends a stable device_id + human name."""
+
+    __tablename__ = "birthday_sync_devices"
+    __table_args__ = (
+        UniqueConstraint("user_id", "device_id", name="uq_birthday_sync_device"),
+    )
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    device_id = Column(String(64), nullable=False)
+    device_name = Column(String(120), nullable=False)
+    last_sync = Column(String(50), nullable=True)  # ISO 8601
+    count = Column(Integer, default=0)
+
+    user = relationship("User")
+
+
 class GroupCalendar(Base):
     """1:1 link between a group and its shared local calendar."""
 
diff --git a/backend/routers/birthdays_router.py b/backend/routers/birthdays_router.py
new file mode 100644
index 0000000..e43ec8e
--- /dev/null
+++ b/backend/routers/birthdays_router.py
@@ -0,0 +1,77 @@
+"""Birthday sync device tracking.
+
+The iOS app reports, after each Contacts birthday sync, which device it was and
+how many birthdays it manages. The web shows this as a "birthdays come from
+these devices" list. Birthday events themselves are ordinary local events
+(see local_router); this router only tracks the sync sources.
+"""
+
+from datetime import datetime, timezone
+
+from fastapi import APIRouter, Depends
+from pydantic import BaseModel
+from sqlalchemy.orm import Session
+
+import models
+from auth import get_current_user
+from database import get_db
+
+router = APIRouter()
+
+
+class SyncReport(BaseModel):
+    device_id: str
+    device_name: str
+    count: int = 0
+
+
+@router.post("/sync-report")
+def report_sync(
+    data: SyncReport,
+    db: Session = Depends(get_db),
+    current_user: models.User = Depends(get_current_user),
+):
+    """Upsert the (user, device) sync record after a Contacts birthday sync."""
+    row = (
+        db.query(models.BirthdaySyncDevice)
+        .filter(
+            models.BirthdaySyncDevice.user_id == current_user.id,
+            models.BirthdaySyncDevice.device_id == data.device_id,
+        )
+        .first()
+    )
+    now = datetime.now(timezone.utc).isoformat()
+    name = (data.device_name or "Gerät")[:120]
+    if row is None:
+        db.add(models.BirthdaySyncDevice(
+            user_id=current_user.id, device_id=data.device_id,
+            device_name=name, last_sync=now, count=data.count,
+        ))
+    else:
+        row.device_name = name
+        row.last_sync = now
+        row.count = data.count
+    db.commit()
+    return {"ok": True}
+
+
+@router.get("/devices")
+def list_devices(
+    db: Session = Depends(get_db),
+    current_user: models.User = Depends(get_current_user),
+):
+    rows = (
+        db.query(models.BirthdaySyncDevice)
+        .filter(models.BirthdaySyncDevice.user_id == current_user.id)
+        .order_by(models.BirthdaySyncDevice.last_sync.desc())
+        .all()
+    )
+    return [
+        {
+            "device_id": r.device_id,
+            "device_name": r.device_name,
+            "last_sync": r.last_sync,
+            "count": r.count,
+        }
+        for r in rows
+    ]
diff --git a/backend/routers/settings_router.py b/backend/routers/settings_router.py
index 049b279..a317846 100644
--- a/backend/routers/settings_router.py
+++ b/backend/routers/settings_router.py
@@ -95,6 +95,21 @@ def update_settings(
     if data.private_event_visibility is not None and data.private_event_visibility not in ("hidden", "busy"):
         raise HTTPException(422, "private_event_visibility must be 'hidden' or 'busy'")
 
+    # A birthday calendar must never become the group-visible ("personal")
+    # calendar — it may be shared directly, but not stand in as your calendar in
+    # group views. Clients filter it out of the picker; this is the safety net.
+    if data.group_visible_calendar_id:
+        bcal = (
+            db.query(models.LocalCalendar)
+            .filter(
+                models.LocalCalendar.id == data.group_visible_calendar_id,
+                models.LocalCalendar.user_id == current_user.id,
+            )
+            .first()
+        )
+        if bcal is not None and bcal.is_birthday:
+            raise HTTPException(422, "A birthday calendar can't be your group-visible calendar")
+
     # For these three override colours, an explicit null is meaningful
     # ("reset to default") and must be persisted as NULL. All other fields
     # keep the previous behaviour where a null/missing value is ignored.
diff --git a/frontend/js/calendar.js b/frontend/js/calendar.js
index e6d43a4..f66dfa1 100644
--- a/frontend/js/calendar.js
+++ b/frontend/js/calendar.js
@@ -3237,7 +3237,9 @@ function renderGroupVisibleList(selectedId) {
   const el = document.getElementById('cfg-group-visible-list');
   if (!el) return;
   el.dataset.selected = (selectedId == null) ? '' : String(selectedId);
-  const own = state.localCalendars.filter(c => c.owned !== false && !c.group);
+  // A birthday calendar may be shared directly, but never stand in as the
+  // group-visible personal calendar.
+  const own = state.localCalendars.filter(c => c.owned !== false && !c.group && !c.is_birthday);
   const selVal = el.dataset.selected;
   const row = (id, name, color) => {
     const val = (id == null) ? '' : String(id);
@@ -3631,7 +3633,26 @@ function renderBirthdaySettings() {
   const colorHint = document.createElement('div');
   colorHint.className = 'form-hint';
   colorHint.textContent = t('birthday_color_hint');
-  container.append(status, notifyWrap, colorHint);
+  const devicesWrap = document.createElement('div');
+  devicesWrap.style.marginTop = '12px';
+  container.append(status, notifyWrap, colorHint, devicesWrap);
+  // Which devices contribute birthdays (from Contacts sync).
+  api.get('/birthdays/devices').then(devs => {
+    if (!Array.isArray(devs) || !devs.length) return;
+    const title = document.createElement('div');
+    title.className = 'panel-desc';
+    title.style.margin = '0 0 4px';
+    title.textContent = t('birthday_devices_title');
+    devicesWrap.appendChild(title);
+    devs.forEach(d => {
+      const rowEl = document.createElement('div');
+      rowEl.className = 'form-hint';
+      rowEl.style.margin = '0 0 2px';
+      const when = d.last_sync ? new Date(d.last_sync).toLocaleDateString() : '';
+      rowEl.textContent = `${d.device_name} — ${t('birthday_devices_count', { n: d.count })}${when ? ' · ' + when : ''}`;
+      devicesWrap.appendChild(rowEl);
+    });
+  }).catch(() => {});
 }
 
 function renderHiddenCalendars() {
diff --git a/frontend/js/i18n.js b/frontend/js/i18n.js
index 90d835b..620edfe 100644
--- a/frontend/js/i18n.js
+++ b/frontend/js/i18n.js
@@ -297,6 +297,8 @@ const translations = {
     birthday_year_ph: 'Jahr',
     birthday_settings_title: 'Geburtstage',
     birthday_color_hint: 'Farbe und Sichtbarkeit änderst du in der Seitenleiste.',
+    birthday_devices_title: 'Geburtstage kommen von diesen Geräten:',
+    birthday_devices_count: '{n} Geburtstage',
     error_name_url: 'Bitte Name und URL eingeben',
     ical_subscribed: '"{name}" abonniert',
     google_synced: 'Kalender synchronisiert',
@@ -639,6 +641,8 @@ const translations = {
     birthday_year_ph: 'Year',
     birthday_settings_title: 'Birthdays',
     birthday_color_hint: 'Change colour and visibility in the sidebar.',
+    birthday_devices_title: 'Birthdays come from these devices:',
+    birthday_devices_count: '{n} birthdays',
     error_name_url: 'Please enter a name and URL',
     ical_subscribed: '"{name}" subscribed',
     google_synced: 'Calendar synced',