LiDAR Motion Alarm

Alarmist: iPhone and iPad LiDAR Motion Detector That Works in Complete Darkness

Point your iPhone or iPad at a doorway, arm the app, and get an immediate loud alarm if anyone enters. LiDAR uses infrared, so it works in complete darkness. One extra layer of security for sleeping in unfamiliar places.

iOSiPadOS

Requires iPhone 12 Pro or newer, or iPad Pro 2020 or newer with LiDAR sensor

Download on the App Store

Alarmist app icon showing LiDAR point cloud with concentric wave arcs

Why I built Alarmist

When I travel, I sometimes sleep in unfamiliar places. Hotels, Airbnbs, guest rooms. I wanted one extra layer of awareness if someone entered the room while I was asleep.

Camera-based motion detection needs visible light. LiDAR does not. The iPhone's LiDAR sensor in iPhone Pro models and iPad Pro fires invisible infrared beams and measures depth. A person walking through a doorway creates a large, sustained depth change that is easy to distinguish from noise.

So I built Alarmist. Position your iPhone or iPad on a stable surface, aim it at the door, and arm the app. If anyone enters, you get an immediate loud alarm that ignores Silent Mode. You will wake up. Optionally, the app can turn on the flashlight and capture a photo when triggered, so you have evidence of what happened.

Complete darkness

LiDAR uses infrared, not visible light. Works when cameras cannot.

Actual depth sensing

Measures real distance changes. A person creates a clear, sustained signal.

Loud alarm

Ignores Silent Mode. You will wake up when motion is detected.

One extra layer

Not a replacement for security systems. Just one more tool in your kit.

LiDAR fires invisible infrared beams and measures depth. When someone enters the detection zone, the depth change triggers an immediate alarm.

Setup view with LiDAR depth dots overlay on doorway — Point at a doorway. LiDAR depth dots show what is being monitored.

Armed mode with dark screen and monitoring status — When armed, screen goes dark to save battery. LiDAR keeps monitoring.

Alarm triggered state with intruder detected — Intruder alert. Loud alarm with optional flashlight and photo capture.

Settings panel with sensitivity and distance controls — Configure sensitivity, distance range, and timing for your environment.

How Alarmist works

Two-stage pipeline: Stage A monitors depth with low power consumption. When motion is detected, Stage B activates the torch, captures evidence, and raises the alarm.

Works in complete darkness

LiDAR uses infrared, not visible light. Monitors the room without any light emission.

Measures actual depth

A person walking creates large, sustained depth changes easy to distinguish from noise.

Loud alarm ignores Silent Mode

You will wake up. The alarm plays at full volume regardless of your phone settings.

Optional flashlight

Automatically turn on the torch when motion is detected to illuminate the intruder.

Evidence capture

Optionally capture a photo when triggered. Evidence saved to your camera roll.

Configurable sensitivity

Adjust detection thresholds to match your environment and reduce false positives.

Temporal smoothing

Require motion in multiple consecutive frames to avoid false alarms from noise.

Important Limitations

Alarmist is not a replacement for proper security systems. It is one extra layer of awareness, not a complete solution.

Device must stay plugged in for extended monitoring. LiDAR and screen-on drain battery quickly.
App must remain in foreground with screen on. Screen lock or switching apps stops monitoring.
Requires LiDAR sensor: iPhone 12 Pro or newer, or iPad Pro 2020 or newer.
Test before relying on it. Every environment is different. Adjust sensitivity and distance bands for your setup.

I built this for my own travel use. It works for me. Test it in your environment before depending on it.

I also enjoy growing dahlias in Beaverton, Oregon

Built by Me (Peter)

I am a bootstrapper who has spent 30 years building products that solve real problems.

Since 1994, I have led three companies from startup to acquisition (Cybersight, Followerwonk, Fluxguard) and built Starbucks' global digital product organization.

One person. No VC money. No growth hacking. I build these apps because I want tools that respect power users.

Download on the App Store