diff --git a/forgetest/forgetest/runner.py b/forgetest/forgetest/runner.py
index 906996c..7a76787 100644
--- a/forgetest/forgetest/runner.py
+++ b/forgetest/forgetest/runner.py
@@ -495,26 +495,37 @@ class Context:
         controller lights the button white for its arm wait and puts it out
         at the press. Without this the notice stood until the test's next
         step, and an operator who still saw it pressed again, which pauses
-        the job. A notice replaced meanwhile is left alone."""
-        with self.run._lock:
-            nid = (self.run.notice or {}).get("id")
+        the job. A notice replaced meanwhile is left alone. The watch lives
+        only as long as the notice it guards and the run: a notice cleared
+        or replaced, a run that finished (passed, failed, or errored before
+        the press) or an abort ends it, so no thread is left polling the
+        LEDs behind a test."""
+        run = self.run
+        with run._lock:
+            nid = (run.notice or {}).get("id")
         if nid is None:
             return
 
+        def standing():
+            with run._lock:
+                return run.finished is None and (run.notice or {}).get("id") == nid
+
         def watch():
             t0 = time.time()
             while hw.button_lit() is not True:
-                if time.time() - t0 > lit_timeout:
+                if not standing() or time.time() - t0 > lit_timeout:
+                    return
+                if run.aborted.wait(0.05):
                     return
-                time.sleep(0.05)
             while hw.button_lit() is not False:
-                if time.time() - t0 > lit_timeout + ARM_PRESS_WAIT_S:
+                if not standing() or time.time() - t0 > lit_timeout + ARM_PRESS_WAIT_S:
                     return
-                time.sleep(0.05)
-            with self.run._lock:
-                same = (self.run.notice or {}).get("id") == nid
+                if run.aborted.wait(0.05):
+                    return
+            with run._lock:
+                same = (run.notice or {}).get("id") == nid
                 if same:
-                    self.run.notice = None
+                    run.notice = None
             if same:
                 self.log("ARM: the button went out at the press; the notice is down")
 
diff --git a/forgetest/tests/test_fixture.py b/forgetest/tests/test_fixture.py
index 46e5150..0e114fb 100644
--- a/forgetest/tests/test_fixture.py
+++ b/forgetest/tests/test_fixture.py
@@ -576,6 +576,24 @@ class RoutingTests(unittest.TestCase):
             lit["v"] = False
             time.sleep(0.3)
             self.assertEqual((run.notice or {}).get("text"), "Something else.")
+            # The watch ends with the run: a test that ends before the press
+            # (a FAIL on the way to the arm, say) leaves no thread polling the
+            # LEDs for up to the arm's whole timeout.
+            def watching():
+                return [t for t in threading.enumerate() if t.name == "forgetest-arm-notice"]
+            deadline = time.time() + 2
+            while watching() and time.time() < deadline:
+                time.sleep(0.02)                         # the earlier watches are gone
+            self.assertFalse(watching())
+            lit["v"] = False
+            self.assertFalse(ctx.arm_press())
+            self.assertTrue(watching())                  # up while the arm is still dark
+            run.finished = {"result": "FAIL", "message": "", "duration_s": 0}
+            deadline = time.time() + 2
+            while watching() and time.time() < deadline:
+                time.sleep(0.02)
+            self.assertFalse(watching())
+            self.assertIsNotNone(run.notice)             # the finished run's notice is left as it was
         finally:
             runner_mod.hw.button_lit = saved