diff --git a/.github/workflows/audit-callers.yml b/.github/workflows/audit-callers.yml
index 3d0b8e7..da42488 100644
--- a/.github/workflows/audit-callers.yml
+++ b/.github/workflows/audit-callers.yml
@@ -20,8 +20,11 @@ name: Audit callers
 # A warning printed into a green run would reproduce the bug it is checking.
 on:
   schedule:
-    # 07:00 UTC daily, before the working day in every timezone the team uses.
-    - cron: "0 7 * * *"
+    # 07:00 UTC on Monday, before the working week starts in every timezone
+    # the team uses. Weekly, because the drift this catches is a rename or a
+    # deleted caller -- a human edit, not a background process -- and every
+    # merge here runs the audit as well.
+    - cron: "0 7 * * 1"
   # AND ON EVERY MERGE, because GitHub disables a SCHEDULED workflow after 60
   # days of repository inactivity -- which would switch this audit off in
   # exactly the silence it exists to detect.
@@ -153,3 +156,28 @@ jobs:
           # check failed for all six SDK repositories and the audit still
           # reported green.
           REVIEWBOT_BOT_TOKEN: ${{ steps.org.outputs.token }}
+
+      # SAY SO, LOUDLY. Email is the only other alert here, and the schedule
+      # is weekly -- a missed email is up to seven days of a repository not
+      # being reviewed while nothing says so. That is the silence this whole
+      # workflow exists to break, so the workflow must not fall into it.
+      #
+      # The same path support-agent, daily-standup and codex-keeper already
+      # use, with the organisation secret every private repository in
+      # MarketData-App already has. No new credential for the alarm: an alarm
+      # with its own secret is an alarm with its own way to fail.
+      #
+      # `if: failure()` rather than `always()`, and `|| true` at the end: the
+      # audit's own verdict stays the job's conclusion. A notifier that can
+      # fail the job would report a Slack outage as fleet drift.
+      - name: Say so, loudly
+        if: failure()
+        env:
+          SLACK_NOTIFY_TOKEN: ${{ secrets.SLACK_NOTIFY_TOKEN }}
+        run: |
+          curl -s -d "Audit callers FAILED. At least one target repository will no longer start a review, and it fails in silence -- every other check there stays green. The run log names the repository and the reason." \
+            -H "Authorization: Bearer ${SLACK_NOTIFY_TOKEN}" \
+            -H "X-workflow: ${GITHUB_WORKFLOW}" \
+            -H "X-repo: ${GITHUB_REPOSITORY}" \
+            -H "X-run_id: ${GITHUB_RUN_ID}" \
+            "https://notify.marketdata.app/slack/notify?type=ci_failure&channel=alerts" || true
diff --git a/README.md b/README.md
index 101c3b2..fb66da0 100644
--- a/README.md
+++ b/README.md
@@ -143,8 +143,11 @@ GITHUB_TOKEN=$(gh auth token) uv run reviewbot audit-callers MarketDataApp/sdk-p
 It exits non-zero when any repository will not start a review, and says why:
 a missing or commented-out `workflow_run`, a name matching no workflow, a
 workflow that does not run on pull requests, or a repository it could not
-read. `.github/workflows/audit-callers.yml` runs it over the whole fleet on a
-daily schedule and on every push to `main`.
+read. `.github/workflows/audit-callers.yml` runs it over the whole fleet every
+Monday at 07:00 UTC and on every push to `main`, and a failure posts to the
+`alerts` Slack channel through the organisation's `SLACK_NOTIFY_TOKEN`. The
+post cannot decide the run's verdict: a Slack outage must not turn a green
+fleet red, and a red run must not read as another outage.
 
 **One monitoring gap, accepted deliberately.** GitHub disables a scheduled
 workflow after 60 days with no activity in its repository, and a workflow
diff --git a/tests/test_callers.py b/tests/test_callers.py
index 07e5d28..17a26ec 100644
--- a/tests/test_callers.py
+++ b/tests/test_callers.py
@@ -341,6 +341,52 @@ def test_the_second_audit_runs_even_when_the_first_fails(audit_workflow):
 # --- fixes from the bot's review of PR #21 ---------------------------------
 
 
+def _alarm_step(spec):
+    steps = spec["jobs"]["audit"]["steps"]
+    found = [s for s in steps if "notify.marketdata.app" in s.get("run", "")]
+    assert found, "the audit has no Slack alarm"
+    return found[0]
+
+
+def test_the_audit_tells_slack_when_it_fails(audit_workflow):
+    # Email is the only other alert, and the schedule is weekly -- so a missed
+    # email is up to seven days of a repository not being reviewed while
+    # nothing says so. An audit against silent failure cannot itself fail
+    # quietly.
+    alarm = _alarm_step(audit_workflow)
+    assert alarm.get("if") == "failure()"
+    assert alarm["env"]["SLACK_NOTIFY_TOKEN"] == "${{ secrets.SLACK_NOTIFY_TOKEN }}"
+
+
+def test_the_alarm_runs_after_both_audits(audit_workflow):
+    # The second audit carries `if: always()`, so it runs after the first
+    # fails. An alarm placed between them would fire while half the fleet is
+    # still unchecked, and report one repository as the whole answer.
+    steps = audit_workflow["jobs"]["audit"]["steps"]
+    audits = [
+        i
+        for i, s in enumerate(steps)
+        if s.get("run", "").strip().startswith("uv run reviewbot audit")
+    ]
+    assert steps.index(_alarm_step(audit_workflow)) > max(audits)
+
+
+def test_the_alarm_cannot_decide_the_jobs_verdict(audit_workflow):
+    # `|| true`, because the audit's own verdict is the answer. Without it a
+    # Slack outage turns a green fleet red, and the next red audit gets read
+    # as another outage.
+    assert _alarm_step(audit_workflow)["run"].rstrip().endswith("|| true")
+
+
+def test_the_alarm_keeps_the_token_out_of_the_url(audit_workflow):
+    # Older callers in the fleet pass `?token=...`. A query string lands in
+    # the run log, in any redirect and in the receiving proxy's access log;
+    # the header does not. New code uses the header.
+    run = _alarm_step(audit_workflow)["run"]
+    assert "Authorization: Bearer ${SLACK_NOTIFY_TOKEN}" in run
+    assert "token=" not in run
+
+
 def test_the_audit_never_runs_on_a_pull_request(audit_workflow):
     # c12ba7a7, and it was a real hole rather than a theoretical one. The job
     # mints installation tokens covering EVERY repository of each owner and