diff --git a/docs/observability.md b/docs/observability.md
index 675a6db..1fddc27 100644
--- a/docs/observability.md
+++ b/docs/observability.md
@@ -548,8 +548,11 @@ So now, if Prometheus stops evaluating, Alertmanager dies, or this host loses
 outbound network, something external notices — in principle. That is the
 failure [#214](https://github.com/Gerrrt/HomeLab/issues/214) lived through from
 the other direction, and the heartbeat is cited as the answer to it in #214's
-own resolution. It is armed and not yet proven: nobody has watched the check go
-red, which is [#288](https://github.com/Gerrrt/HomeLab/issues/288).
+own resolution. It is armed and proven: on 2026-09-09 Alertmanager was stopped
+for 18 minutes, the check went red and emailed, and the first ping after the
+restart landed within two minutes; the daily route was confirmed the same
+sitting ([#288](https://github.com/Gerrrt/HomeLab/issues/288), times in the
+runbook).
 
 `check_alert_channels.py --live` reports the destination on every deploy,
 classifying the heartbeat's host as a watcher or a push service. A push service
diff --git a/docs/roadmap.md b/docs/roadmap.md
index b51702d..83f1f7f 100644
--- a/docs/roadmap.md
+++ b/docs/roadmap.md
@@ -1080,7 +1080,7 @@ them name the condition that would change the answer.
       deliberately sends no test notification. A check that depends on the
       delivery path inherits the blind spot that made this last ten hours. Every
       assertion reads a file. The dead man's switch is the other half of the
-      answer and remains untested — #288.
+      answer; it was armed and then tripped on purpose on 2026-09-09 — #288.
 
       All three failure paths were exercised rather than assumed: a `url_file`
       with no renderer, a rendered-but-empty file, and a container that cannot
diff --git a/docs/runbooks/verify-the-alert-path.md b/docs/runbooks/verify-the-alert-path.md
index 692d416..3d17bb0 100644
--- a/docs/runbooks/verify-the-alert-path.md
+++ b/docs/runbooks/verify-the-alert-path.md
@@ -42,10 +42,10 @@ travel, but nothing machine-checks its absence — you do.
 > absence, and passes. From 2026-09-07 to this date the URL pointed at `ntfy.sh`
 > like every other receiver, and there was no dead man's switch, only a
 > heartbeat nobody was waiting on
-> ([#359](https://github.com/Gerrrt/HomeLab/issues/359)). **The drill below has
-> still not been run** — that is [#288](https://github.com/Gerrrt/HomeLab/issues/288),
-> and until it has, "the check goes red when the stack dies" is a claim, not an
-> observation.
+> ([#359](https://github.com/Gerrrt/HomeLab/issues/359)). **The drill below was
+> run the same day** — [#288](https://github.com/Gerrrt/HomeLab/issues/288) —
+> so "the check goes red when the stack dies" is an observation, with times,
+> under *Confirming it actually works*.
 
 The watcher has to live somewhere other than the monitoring host. A watcher on
 this host fails at the same moment as the thing it is watching, which is not
@@ -117,6 +117,25 @@ it. Nothing enforces that from here, which is why it is written down.
 
 ## Confirming it actually works
 
+> **Done 2026-09-09**, both halves in one sitting, read off the monitoring host
+> with the phone in hand ([#288](https://github.com/Gerrrt/HomeLab/issues/288)):
+>
+> | | |
+> | --- | --- |
+> | `docker stop alertmanager` | 03:07:37 UTC, seconds after a ping went out |
+> | Check DOWN, email received | 03:25:58 UTC — 18 minutes; period 5m + grace 15m says 20 at most |
+> | `docker start alertmanager` | 03:25:58 UTC, ready 5 s later |
+> | First ping after restart | 03:27:57 UTC — 2 minutes, inside one `repeat_interval` |
+> | Second Watchdog route at 2m, `make reload` | 03:28:29 UTC |
+> | Watchdog on the normal ntfy channel | 03:28 UTC, on the phone |
+> | Route back to 24h, `make reload` | 03:33:16 UTC |
+>
+> Zero delivery failures across the whole window. One thing the daily half
+> showed on the way: a route with `repeat_interval` below the root's
+> `group_interval` (5m) repeats on the 5m tick, not at its own interval — the
+> same coupling the heartbeat route works around above. It does not affect the
+> 24h route, and the first notification still went out immediately.
+
 Do not trust a green check you have never seen go red.
 
 ```bash
diff --git a/scripts/check_alert_channels.py b/scripts/check_alert_channels.py
index 89da3cc..564f05b 100755
--- a/scripts/check_alert_channels.py
+++ b/scripts/check_alert_channels.py
@@ -47,8 +47,8 @@
 assertion here reads a file, and none of them needs a notification to succeed.
 
 The dead man's switch is the other half of the answer and is not this: it is what
-notices when the whole path is down, and whether it actually works has never been
-tested (#288).
+notices when the whole path is down. It was tripped on purpose on 2026-09-09 and
+did (#288); the times are in docs/runbooks/verify-the-alert-path.md.
 
 Usage: scripts/check_alert_channels.py [--files] [--live] [STACK]
 """