Tunk

Knock twice on your MacBook.

Tunk feels the knock through the accelerometer already inside the machine, at 796 Hz, and fires the shortcut you chose. It is Back Tap on an iPhone, applied to a laptop. It reads that one sensor and nothing else.

Download the build See the measurements

4.6 MB · Apple silicon · macOS 13 or later.

Not a mock-up. The monitor drawing real knocks, at 796 Hz, while the counter moves.

Try the gesture.

Two knocks inside 400 ms, which is the window the detector joins. One knock on its own ripples and does nothing, the same way the app treats it.

An open MacBook seen from directly above on a dark desk, with two amber points of light blooming out of the aluminium palm rest beside the trackpad.

Knock twice on the photograph to wake the screen. Knock twice again to put it back.

Three screens, no manual.

Turn detection on and watch taps land. Choose what a double tap does. Teach it how hard you knock. Everything an experiment rather than a feature lives under Advanced, switched off.

Tunk settings, General: an enable switch, live sample rate, taps fired, last latency, and a tap monitor drawing onsets.
General The tap monitor draws every onset as it lands. A grey spike is one the typing gate ate on purpose.
Tunk settings, Actions: double tap and single tap, each bound to a hotkey, a Shortcut, or nothing.
Actions A hotkey or any macOS Shortcut. Single tap ships unbound, because one knock is a mug set down.
Tunk settings, Calibration: a learned threshold, a sensitivity slider, and a slider for how long to ignore taps after typing.
Calibration The threshold comes from your own taps. Coupling changes with the machine and the surface.

Measured, not claimed.

796 Hz
sensor rate, measured
209 ms
latency p95, second tap to key
0
false triggers, held out
16/20
on a lap, still failing

On a hard desk and on a soft surface the detector finds 20 of 20 held-out double-taps. On a lap it finds 16, against a bar of 98 %, so the harness returns FAIL. The typing metric, the one that decides whether this is worth running, has never been graded out of sample and reads INCOMPLETE. Both numbers are here because hiding the second would make the first worthless.

Running in four steps.

  1. Open the DMG and drag Tunk onto Applications.
  2. Open it from Applications. Tunk lives at the right-hand end of the menu bar and has no Dock icon.
  3. Grant two permissions. A window opens on first launch: Input Monitoring to read the accelerometer, Accessibility to press the key. Each row opens the right pane for you, and the window notices the moment you come back.
  4. Double-tap the case. Palm rest, lid, or the deck beside the trackpad. The ring lights up for each knock it hears.

Tunk 0.1.0

4.6 MB · Apple silicon · macOS 13 or later
sha256 d285a62f2fe402ab…

Download the DMG

This build is signed ad hoc, not with a Developer ID. On a Mac that is not the one it was built on, macOS will refuse to open it and say it cannot verify the developer. Opening it from the right-click menu is the usual way past that, and a notarised build is the real fix. It is also why macOS asks for both permissions again after every update: a grant belongs to one signature, and each build makes a new one.