diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 4c5ceb4..2ed575c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -290,6 +290,8 @@ jobs:
         run: node test/live-resize.js
       - name: The activation policy before launch — APPKIT_ACTIVATION_POLICY and runMain({ activationPolicy })
         run: node test/activation-policy.js
+      - name: The session's idle time — lastInputMs, before initApp and from a worker
+        run: node test/last-input.js
       - name: A worker that ends with answers in flight, from its own thread and others — dropped, not a fatal error or an abort
         run: node test/ending-worker.js
 
diff --git a/README.md b/README.md
index f122136..c62dfca 100644
--- a/README.md
+++ b/README.md
@@ -125,7 +125,7 @@ waits on the UI thread (`test/threaded-verbs.js` covers each row):
 
 | from a worker | verbs |
 | --- | --- |
-| unchanged, on the calling thread | surfaces and video surfaces, every `ctx*` (`ctxDrawSymbol` included), layouts and fonts, `symbolSize`, `pasteboardTypeForMIME`, `pasteboardTypeInfo`, `contentTypeFor`, `colorSpace` |
+| unchanged, on the calling thread | surfaces and video surfaces, every `ctx*` (`ctxDrawSymbol` included), layouts and fonts, `symbolSize`, `pasteboardTypeForMIME`, `pasteboardTypeInfo`, `contentTypeFor`, `colorSpace`, `lastInputMs` |
 | a command, answering nothing | `initApp`, `setActivationPolicy`, `setAppName`, `activateApp`, `showWindow`, `hideWindow`, `setWindowFrame`, `setWindowTitle`, `setWindowMinMax`, `setWindowIgnoresMouseEvents`, `invalidateWindowShadow`, `destroyWindow2`, `setCursor`, `setMainMenu`, `setDockMenu`, `setDockBadge`, `cancelUserAttention`, `setStatusItem`, `setStatusItemMenu`, `removeStatusItem`, `registerDropTypes`, `setDropResponse`, `pasteboardWriteText`, `pasteboardWrite`, `pasteboardClear`, `cancelPanel`, `cancelPopUpMenu`; the test posts `postMouseEvent`, `postKeyEvent`, `postAppleEvent`, `postAccessibilityDisplayChange` |
 | a handle at the call | `createWindow2`, followed by `window-created { handle, windowNumber }`; every event about the window, input included, carries `handle`, so `ev.handle === win` |
 | | `windowRootLayer`, allocated with the window |
@@ -1599,6 +1599,23 @@ Mechanism only: what to do with `reduceMotion` is the renderer's (react-x11: loo
 so the observer path can be exercised without touching the user's settings — test-only, like
 `postAppleEvent`; `test/accessibility-display.js` is the check.
 
+## Idle time (an empty desk)
+
+How long the user has been away from the keyboard and pointer, across the whole session and
+every app — the clock a screen saver keys off (react-x11's `useIdle`,
+[react-x11#951](https://github.com/sidorares/react-x11/pull/951)):
+
+```js
+native.lastInputMs();   // -> 41250.3: ms since the last keyboard, mouse, trackpad or tablet event
+```
+
+It is `CGEventSourceSecondsSinceLastEventType(kCGEventSourceStateCombinedSessionState,
+kCGAnyInputEventType)`, in milliseconds. There is no event: poll it. It asks nothing of AppKit and
+needs no permission, so it answers synchronously on whichever thread calls it — before
+`initApp`, in pump mode, and from a worker with the main thread parked in `runMain`. It is not
+`ioreg`'s `HIDIdleTime`: the two are kept apart, and while they agree at a desk, on CI's VMs this
+one ran 3–5 s longer. `test/last-input.js` is the check.
+
 ## Mapping to a React reconciler
 
 The shape of a host config on top of this:
diff --git a/package.json b/package.json
index fa708cb..d5a3ee7 100644
--- a/package.json
+++ b/package.json
@@ -43,7 +43,7 @@
     "install": "node scripts/install.js",
     "build": "node-gyp rebuild",
     "demo": "node demo/demo.js",
-    "test": "node test/app-lifecycle.js && node test/animation.js && node test/layer-transform.js && node test/contents-gravity.js && node test/contents-center.js && node test/accessibility-display.js && node test/ignores-mouse-events.js && node test/popup-menu.js && node test/pasteboard-write.js && node test/surface-blit.js && node test/surface-faded.js && node test/image-smoothing.js && node test/surface-colorspace.js && node test/video-surface.js && node test/player.js && node test/round-rect-xy.js && node test/clip-rule.js && node test/radial-gradient.js && node test/control-bezels.js && node test/text-features.js && node test/font-from-data.js && node test/text-coverage.js && node test/text-typesetter.js && node test/text-line-height.js && node test/text-line-width.js && node test/text-justify.js && node test/text-scale.js && node test/symbols.js && node test/eventkit-permissions.js && node test/calendars.js && node test/calendar-writes.js && node test/screencolor.js && node test/notifications.js && node test/threaded.js && node test/threaded-verbs.js && node test/threaded-frames.js && node test/threaded-resize.js && node test/ending-worker.js && node test/live-resize.js && node test/activation-policy.js"
+    "test": "node test/app-lifecycle.js && node test/animation.js && node test/layer-transform.js && node test/contents-gravity.js && node test/contents-center.js && node test/accessibility-display.js && node test/ignores-mouse-events.js && node test/popup-menu.js && node test/pasteboard-write.js && node test/surface-blit.js && node test/surface-faded.js && node test/image-smoothing.js && node test/surface-colorspace.js && node test/video-surface.js && node test/player.js && node test/round-rect-xy.js && node test/clip-rule.js && node test/radial-gradient.js && node test/control-bezels.js && node test/text-features.js && node test/font-from-data.js && node test/text-coverage.js && node test/text-typesetter.js && node test/text-line-height.js && node test/text-line-width.js && node test/text-justify.js && node test/text-scale.js && node test/symbols.js && node test/eventkit-permissions.js && node test/calendars.js && node test/calendar-writes.js && node test/screencolor.js && node test/notifications.js && node test/threaded.js && node test/threaded-verbs.js && node test/threaded-frames.js && node test/threaded-resize.js && node test/ending-worker.js && node test/live-resize.js && node test/activation-policy.js && node test/last-input.js"
   },
   "dependencies": {
     "node-addon-api": "^8.3.0"
diff --git a/src/backend.mm b/src/backend.mm
index 75798a9..da6fa89 100644
--- a/src/backend.mm
+++ b/src/backend.mm
@@ -6929,6 +6929,22 @@ static void Apply(void* info, const CGPathElement* e) {
                            (double)NSPasteboard.generalPasteboard.changeCount);
 }
 
+// ---------------------------------------------------------------------------
+// idle time
+// ---------------------------------------------------------------------------
+
+// lastInputMs() -> number: milliseconds since the last input event of any
+// kind in the login session — keyboard, mouse, trackpad, tablet — from any
+// app, the clock a screen saver keys off. CGEventSource keeps it per session,
+// so it asks nothing of AppKit or the window server's event stream and needs
+// no permission; it answers on whichever thread calls it, before initApp
+// and from a worker alike.
+static Napi::Value LastInputMsFn(const Napi::CallbackInfo& info) {
+  CFTimeInterval s = CGEventSourceSecondsSinceLastEventType(
+      kCGEventSourceStateCombinedSessionState, kCGAnyInputEventType);
+  return Napi::Number::New(info.Env(), s * 1000.0);
+}
+
 // ---------------------------------------------------------------------------
 // screens + cursors + appearance
 // ---------------------------------------------------------------------------
@@ -8060,6 +8076,7 @@ void InitBackend(Napi::Env env, Napi::Object exports) {
   BFN("pasteboardReadText", PbReadTextFn);
   BFN("pasteboardClear", PbClearFn);
   BFN("pasteboardChangeCount", PbChangeCountFn);
+  BFN("lastInputMs", LastInputMsFn);
   BFN("setMainMenu", SetMainMenuFn);
   BFN("mainMenuInfo", MainMenuInfoFn);
   BFN("activateMenuItem", ActivateMenuItemFn);
diff --git a/test/last-input.js b/test/last-input.js
new file mode 100644
index 0000000..e3c2e42
--- /dev/null
+++ b/test/last-input.js
@@ -0,0 +1,76 @@
+'use strict';
+// lastInputMs (react-x11#951's bridge follow-up): the session's idle time,
+// read the way a screen saver reads it. A test cannot make or withhold the
+// user's input, so what is checked is what holds whatever they do. Exits 0
+// when every expectation held.
+//
+// Checked: before initApp it answers a finite, non-negative number; between
+// two reads it either grew by the time between them or was reset by input
+// since; and from a worker, with the main thread parked in runMain, it
+// answers synchronously on the worker's thread. IOHIDSystem's HIDIdleTime is
+// printed beside it, not compared: the two are kept apart, and on CI's VMs
+// this one ran 3-5 s longer than HIDIdleTime read just before it.
+
+const { execFileSync } = require('child_process');
+const fs = require('fs');
+const { Worker, isMainThread } = require('worker_threads');
+const { native } = require('..');
+
+const say = (s) => fs.writeSync(2, `last-input: ${s}\n`);
+const fail = (msg) => {
+  say(`FAIL ${msg}`);
+  process.exit(1);
+};
+const TOL = 50;
+
+const isIdleTime = (v) => typeof v === 'number' && Number.isFinite(v) && v >= 0;
+
+const blockFor = (ms) => {
+  const until = Date.now() + ms;
+  while (Date.now() < until);
+};
+
+function hidIdleMs() {
+  const out = execFileSync('/usr/sbin/ioreg', ['-c', 'IOHIDSystem', '-r', '-d', '1', '-k', 'HIDIdleTime'], {
+    encoding: 'utf8',
+  });
+  const m = /"HIDIdleTime"\s*=\s*(\d+)/.exec(out);
+  return m ? Number(m[1]) / 1e6 : null;
+}
+
+if (isMainThread) {
+  // 1. before initApp, synchronously
+  const first = native.lastInputMs();
+  if (!isIdleTime(first)) fail(`lastInputMs() before initApp: ${first}`);
+
+  // 2. a clock: it grew by the time between the reads, or input reset it
+  const t0 = Date.now();
+  const a = native.lastInputMs();
+  blockFor(300);
+  const b = native.lastInputMs();
+  const elapsed = Date.now() - t0;
+  const grew = Math.abs(b - a - elapsed) <= TOL;
+  const reset = b <= elapsed + TOL;
+  if (!grew && !reset) fail(`two reads ${elapsed} ms apart: ${a} then ${b}`);
+
+  // 3. beside the HID idle time, for the log
+  const hid = hidIdleMs();
+  say(`lastInputMs ${native.lastInputMs().toFixed(0)} ms, HIDIdleTime ${hid == null ? 'none' : hid.toFixed(0) + ' ms'}`);
+
+  // 4. from a worker, the main thread parked
+  native.initApp();
+  new Worker(__filename).on('error', (e) => fail(e && e.stack ? e.stack : e));
+  const code = native.runMain();
+  if (code !== 0) fail(`runMain returned ${code}`);
+  say('ok');
+  process.exit(0);
+} else {
+  native.connect(() => {});
+  const v = native.lastInputMs();
+  if (!isIdleTime(v)) {
+    say(`FAIL lastInputMs() from a worker: ${v}`);
+    native.requestExit(1);
+  } else {
+    native.requestExit(0);
+  }
+}