Tripwire
Point your webcam at a door, hallway, or chair. When motion crosses the frame, Tripwire announces whoever walked in like a sarcastic royal herald. Free, no signup, video never leaves your browser.
How Tripwire works
Tripwire uses your webcam and the browser's Web Video API to detect motion in the camera frame. It compares each video frame to the previous one — when enough pixels have changed (someone walking, a door opening, a hand waving), Tripwire considers that a "trip" and announces it.
The motion analysis runs entirely in your browser using a tiny canvas. Frames are downsampled to 160×90 pixels and compared frame-by-frame. The video itself is never uploaded, recorded, saved, or sent anywhere.
What devices work?
Anything with a camera. Tripwire is just a webpage — works on any device with a camera and a modern browser. Confirmed working on:
- iPhone & Android phones — prop the phone facing the door (rear camera works best)
- MacBooks (Air, Pro, any year) — built-in FaceTime camera
- iPads & Android tablets — front or back camera
- Windows / Linux / Chromebook laptops — built-in webcam
- Any USB webcam plugged into a desktop PC
- Browser-recognized virtual cameras (OBS Virtual Camera, etc.)
Browsers tested: Chrome, Safari, Firefox, Edge, Brave, Arc. Mobile Safari and Chrome both work — just grant camera permission when prompted.
Tip: on a phone, prop it horizontally (landscape) at the doorway for the cleanest motion-detection frame.
Privacy
The camera feed is processed entirely on the client side via getUserMedia + canvas frame analysis. No video data is uploaded, recorded, or persisted in any way. We have no servers receiving frames. The mirror-flipped preview you see is just so you can frame your shot — even that preview is local.
You can revoke camera permission at any time from the address-bar lock icon. Tripwire stops the moment you do.
Tips for best detection
- Steady camera. Even small camera shake registers as motion. Prop the device on something solid.
- Decent lighting. Very dark scenes cause noisy false triggers from sensor static.
- Sensitivity slider. Lower it if the door slamming on its own is enough to trigger. Raise it if subtle walks aren't catching.
- 5-second cooldown. After a trip, Tripwire pauses for 5 seconds so it doesn't keep narrating one continuous walk-by.
- Calibration. When you click "Arm tripwire", Tripwire spends 2 seconds measuring background noise to set its baseline.
FAQ
Does Tripwire identify who walked in?
No. It just detects motion. The "herald" is generic mocking — it has no idea who you are or who walked in. That's why the lines are insults.
Can I use this with a security camera or external webcam?
Yes — any USB webcam, internal camera, or virtual camera input that the browser sees as a video device works.
Does it work on phones?
Yes — the browser's webcam permission works on mobile too. You can prop your phone with the front camera facing a doorway.
Will the speaker scare the person walking in?
That's the whole point.