Yowl — MacBook theft alarm

A menu-bar alarm that makes stealing your MacBook loud.

Free and open source (MIT). No accounts, no analytics, no servers.

dontstealmylaptop.com — download, and a walkthrough of what a theft looks like.

Arm it when you leave your laptop on a café table. If someone unplugs the charger, closes the lid, or picks the machine up, it screams at full volume — over mute, over headphones — locks the screen, and photographs whoever is in front of it. Only unlocking your Mac stops it.

What it is not

This is a deterrent, not a recovery system. Turn on Find My and FileVault — those are what actually recover or protect a stolen Mac. Yowl makes the theft loud and public, which is a different job.

Triggers

Motion and lid are off by default because each can fire in ordinary use — closing your own laptop is not theft.

When it fires

• Siren at forced maximum volume, out of the built-in speakers, overriding mute and any connected headphones.
• Screen lock, so nobody browses your open session while it screams.
• Photographs (optional) of whoever is there, including the ten seconds before the alarm — often the more useful shot, since it catches someone walking up rather than the back of their head.
• A push to your phone (optional) with the photos, via your own private ntfy.sh link.

Why the source is open

The app asks for your camera and can send photographs to your phone. You are being asked to trust a stranger's binary with that. The source is here so you do not have to — you can check the two claims that matter in about a minute:

# All networking. One implementation, and the one line that builds it.
grep -rn "URLSession\|NWConnection\|CFStream" Sources/
#   Sources/AlarmCore/Alerts/AlertTransport.swift  — the only HTTP client
#   Sources/AlarmApp/AppModel.swift                — constructs it, once

# What the shipped app is actually allowed to do.
codesign -d --entitlements - /Applications/Yowl.app
#   com.apple.security.device.camera
#   com.apple.security.network.client

That client is used in exactly one place: sending an alert to the ntfy link you chose, and only when you have switched phone alerts on. There is no other network code, no analytics SDK, and no telemetry to find.

Privacy

No accounts, no analytics, no servers of our own. Photographs are written to ~/Library/Application Support/Yowl/Evidence, capped at the 40 most recent.

Nothing leaves your Mac unless you switch on phone alerts, which send the alarm and up to three photos to your own private ntfy.sh link. That link's name is 128 bits of randomness and is the access control — treat it like a password, and rotate it from Settings if it leaks. ntfy deletes attachments after a few hours, so the copies on your Mac are the durable ones.

See PRIVACY.md.

Known limitations, stated plainly

• Repetitive backgrounds confuse motion detection. Window blinds, tiled floors and brick make the camera unable to tell a passer-by from the laptop being moved. Use the sensitivity test in Settings at your actual table: if waving your hand moves the number, don't rely on motion detection there.
• Quitting the app stops the alarm. The Quit menu item is disabled while armed, but ⌘Q and Force Quit still work. Your audio settings are restored either way.
• A thief can hold the power button. Nothing in userspace prevents that.

Install

Download Yowl 1.3.1 — 1.2 MB, signed and notarised by Apple, so it opens with a double-click. Drag it to Applications.

Or build it yourself; it takes about a minute and needs nothing but Xcode.

You need: macOS 14 or later, and Xcode 16 or later (or just the Command Line Tools) for Swift 6.2+. Built and tested on Swift 6.3.3 / Xcode 26.6.

git clone https://github.com/nejcar20/yowl.git
cd yowl
swift test                  # 270 tests, ~30s the first time
./Scripts/make-bundle.sh    # produces build/Yowl.app
open build/Yowl.app

Move build/Yowl.app to /Applications if you want to keep it.

First run

Yowl lives in the menu bar — no Dock icon and no window. Look for the shield icon; everything is behind it.

• It asks for camera access the first time you switch on a camera feature (the motion trigger, or photographs). Nothing camera-related runs until you do.
• If you have no Apple Development certificate on your Mac, the build script signs the app ad-hoc and says so. Everything works, but macOS ties camera permission to the signature, so it will ask again after every rebuild.
• Nothing is armed until you press Arm.

Requirements

macOS 14 or later. Universal binary — Apple Silicon and Intel. The lid trigger needs the hinge angle sensor, which Intel Macs do not have; it stays hidden there. Everything else works on both.

Closing the lid all the way

Closing the lid begins a sleep, and the audio hardware powers down at the start of that transition — measured directly: lid shut, Mac held awake by a deferred sleep, output device present, volume 1.0, mute cleared four times a second, engine running, and silence. Deferring the sleep is not enough. The sleep has to not begin.

The setting that prevents it is pmset disablesleep, which is root-only. So Keep screaming with the lid closed is off by default, and switching it on asks once for an administrator password to install one rule:

<you> ALL=(root) NOPASSWD: /usr/bin/pmset -a disablesleep 1, \
                           /usr/bin/pmset -a disablesleep 0

Two absolute paths, fixed arguments, scoped to your account, validated with visudo -c before install and again after. Nothing else is granted, and /etc/sudoers.d/yowl-disablesleep can be deleted at any time.

The hold is taken once when the siren starts and lasts as long as you choose in Settings — 30 seconds, 1, 2 or 5 minutes, defaulting to a minute. The ceiling is not adjustable: every extra minute is another minute a laptop shut in a bag cannot sleep, which is a thermal question rather than a preference. It is deliberately not renewed — a minute makes someone put the laptop down, while an alarm that kept a bagged machine awake indefinitely would be the more dangerous failure. A detached watchdog releases it even if the app is force quit, and disarming releases it at once.

Why it is not on the Mac App Store

Locking the screen has no public API, so Yowl calls a private one — an automatic rejection. A Store build would also lose the lid trigger (raw IOKit HID access is not grantable under the sandbox) and the unlock-to-disarm behaviour (sandboxed apps do not receive the screen-unlock notification), which would put the passcode back. That is most of the reason the app is worth running, so it is distributed directly instead: signed with a Developer ID certificate and notarised by Apple, which is what lets the download open without a warning.

Releases are cut with ./Scripts/release.sh <version> — build, sign, notarise the app, staple it, package and sign the image, notarise and staple that too.

Contributing

Bug reports are more useful than features right now. In particular:

• Does motion detection work at your desk? Use "Test sensitivity" in Settings, wave your hand, and tell me the number. Repetitive backgrounds (blinds, tiles, brick) are known to defeat it and I would like real data on how common that is.
• Did the alarm ever fire when it should not have? That is the failure that matters most.

The test suite is the contribution guide: swift test runs 241 tests, and anything touching a trigger, a response, or the privacy-facing behaviour needs one that fails when the change is reverted. Several bugs in this codebase shipped behind tests that passed against broken code, so that bar is deliberate.

License

MIT — see LICENSE.

Contact

jernejkocica@gmail.com — bug reports are better filed as issues, but mail works.