diff --git a/src/bubo/analytics.py b/src/bubo/analytics.py
index b101cb1..acb4f75 100644
--- a/src/bubo/analytics.py
+++ b/src/bubo/analytics.py
@@ -39,6 +39,7 @@
 import threading
 import uuid
 from collections.abc import Iterable
+from datetime import UTC, datetime
 from pathlib import Path
 from typing import Any
 from urllib.request import Request, urlopen
@@ -203,6 +204,9 @@ def __init__(self, config, event, properties):
 _install_node: int | None = None
 _identity_lock = threading.Lock()
 _surface = "unknown"
+# UTC days this process sent session_start on; the service polls in-process.
+_session_days: set[str] = set()
+_session_lock = threading.Lock()
 
 # Only these labels may leave the machine; paths are used locally and discarded.
 _LANGUAGES = {
@@ -456,8 +460,24 @@ def track(cfg: AnalyticsConfig, event: str, **props: Any) -> None:
     _emit(cfg, event, props)
 
 
+def _utc_day() -> str:
+    return datetime.now(UTC).date().isoformat()
+
+
 def record_session_start(cfg: AnalyticsConfig, *, scm_provider: str, projects_count: int) -> None:
-    """One event per poll cycle start — liveness + install context."""
+    """Liveness + install context: once per process per UTC day.
+
+    The service calls ``poll()`` every few minutes in one process; sending
+    this per poll made it the bulk of all events. Once a day still shows a
+    long-running idle service as alive. A day isn't spent while consent is off.
+    """
+    if not analytics_enabled(cfg):
+        return
+    day = _utc_day()
+    with _session_lock:
+        if day in _session_days:
+            return
+        _session_days.add(day)
     _emit(
         cfg,
         "session_start",
diff --git a/tests/conftest.py b/tests/conftest.py
index d2e775b..940251a 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -64,6 +64,7 @@ def offline():
     posthog.configure_otel(TelemetryConfig(analytics=AnalyticsConfig(enabled=False)))
     with analytics._pending_lock:
         analytics._pending_events.clear()
+    analytics._session_days.clear()
     assert not attempted, "A test attempted external telemetry without a fake transport"
 
 
diff --git a/tests/test_session_start.py b/tests/test_session_start.py
new file mode 100644
index 0000000..88064d9
--- /dev/null
+++ b/tests/test_session_start.py
@@ -0,0 +1,72 @@
+"""``session_start`` is a liveness signal, not a per-poll event.
+
+The service calls ``poll()`` in one process every few minutes. Drives the
+real ``poll()`` with an idle config and counts the queued PostHog events.
+"""
+
+from __future__ import annotations
+
+import tempfile
+from collections.abc import Iterator
+from contextlib import contextmanager
+from pathlib import Path
+from unittest.mock import MagicMock, patch
+
+from bubo import analytics, db, paths, poller
+from bubo.analytics_config import AnalyticsConfig
+from bubo.review_config import ReviewConfig
+
+CONSENT = AnalyticsConfig(enabled=True, endpoint="https://posthog.invalid/batch", api_key="k")
+
+
+@contextmanager
+def _state() -> Iterator[None]:
+    old = paths.DB
+    try:
+        with tempfile.TemporaryDirectory() as tmp:
+            paths.DB = Path(tmp) / "state" / "reviewer.sqlite"
+            paths.DB.parent.mkdir()
+            db.init_db()
+            yield
+    finally:
+        paths.DB = old
+
+
+def _session_starts(cfg: ReviewConfig, polls: int, days: list[str] | None = None) -> int:
+    provider = MagicMock()
+    provider.name = "github"
+    provider.token.return_value = "t"
+    with (
+        _state(),
+        patch.object(poller, "read_config", return_value=cfg),
+        patch.object(poller, "get_provider", return_value=provider),
+        patch.object(analytics, "flush"),
+        patch.object(analytics, "_utc_day", side_effect=days or ["2026-10-20"] * polls),
+    ):
+        for _ in range(polls):
+            poller.poll(worker_mode="inline")
+    with analytics._pending_lock:
+        return sum(
+            1 for *_, queued in analytics._pending_events if queued["event"] == "session_start"
+        )
+
+
+def _idle() -> ReviewConfig:
+    return ReviewConfig(provider="github", projects=[], analytics_config=CONSENT)
+
+
+def test_repeated_polls_in_one_process_send_one_session_start() -> None:
+    assert _session_starts(_idle(), polls=3) == 1
+
+
+def test_a_long_running_service_still_checks_in_once_a_day() -> None:
+    days = ["2026-10-20", "2026-10-20", "2026-10-21", "2026-10-21"]
+    assert _session_starts(_idle(), polls=4, days=days) == 2
+
+
+def test_session_start_is_not_spent_while_analytics_is_off() -> None:
+    off = ReviewConfig(
+        provider="github", projects=[], analytics_config=AnalyticsConfig(enabled=False)
+    )
+    assert _session_starts(off, polls=1) == 0
+    assert _session_starts(_idle(), polls=1) == 1