Can Your iPhone Replace a Security Camera? Camera vs LiDAR for Motion Detection

January 10, 2026

Somewhere in a drawer you have an old iPhone. And at some point you've thought: "Can I just use this as a security camera?"

The answer is yes, sort of. There are a dozen apps on the App Store that turn an iPhone into a security camera. They work fine in daylight. They stream video to your other devices. They detect motion and send notifications.

But they all share the same problem.

Traditional security cameras, and the iPhone camera apps that imitate them, share the same fundamental dependency: they need light to see.

The problem with camera-based motion detection

A camera captures reflected visible light and turns it into an image. Motion detection on top of that image works by comparing consecutive frames: if enough pixels change, something moved.

This works well in good lighting. But it comes with baggage:

Darkness kills it. Turn off the lights and the camera sees a black rectangle. Some security camera apps use the iPhone flashlight as a makeshift IR illuminator, but that's a bright visible light that defeats the purpose if you're trying to sleep.

Light changes cause false positives. Car headlights sweep across the wall. A cloud passes over the moon. The heater turns on and the curtains shift. A camera sees all of these as "motion" because the pixels changed. The camera doesn't know the difference between a shadow and a person.

It requires a second device for monitoring. If you're using your old iPhone as the camera, you need your current phone (or a laptop) to receive the alerts. Two devices, both charged, both connected to the same network.

This is what a camera sees when the lights are off. The only detail is light leaking through the blinds. A person walking through this room is invisible to any camera-based detection app.

What LiDAR does differently

If your iPhone has a LiDAR sensor (iPhone 12 Pro or newer, iPad Pro 2020+), it has a completely different option for motion detection. LiDAR doesn't capture images. It fires invisible infrared pulses and measures how long they take to bounce back. The result is a depth map: a 3D measurement of how far away every surface is.

This changes the equation:

Works in total darkness. The infrared pulses are invisible to the human eye. No light source needed. The room stays dark. You can sleep.

Immune to light-based false positives. Shadows don't have depth. Headlights through the window don't change the distance to the wall. LiDAR measures physical distance, not brightness. A person walking through a doorway creates a large, sustained change in the depth reading. Nothing else does.

Single device. The same phone that runs the LiDAR sensor also sounds the alarm. No second device, no network dependency, no streaming.

The comparison

Camera wins on remote monitoring and daytime use. LiDAR wins on the scenarios that matter for sleeping in a dark room: darkness, false positives, and zero extra hardware.

Let me break this down honestly:

Camera wins at:

• Daylight motion detection. In a well-lit room, camera-based detection works well and gives you a video feed.
• Remote monitoring. Stream the feed to another device. Watch from anywhere. LiDAR apps don't do this because they're measuring depth, not capturing video.
• Evidence quality. A camera gives you a recognizable image or video of whoever entered. LiDAR gives you a depth silhouette. If you need to identify someone, camera wins.
• Continuous recording. Some camera apps record 24/7 and let you scrub through footage. LiDAR apps trigger on motion but don't maintain a continuous feed.

LiDAR wins at:

• Darkness. Not close. Camera sees nothing. LiDAR sees everything. If you're monitoring a room while you sleep with the lights off, there's no contest.
• False positive rate. Camera-based detection triggers on every shadow, headlight, and lighting change. LiDAR only triggers on actual physical objects entering the detection zone. In practice, this is the difference between sleeping through the night and getting woken up by a passing car.
• No extra hardware. One phone. On the nightstand. No second phone, no wifi streaming, no camera mount.
• Privacy. LiDAR produces depth data, not images. No video of you sleeping. No footage that could be compromised.

When to use a camera

Use an old iPhone as a security camera when:

• The room is lit (or you're OK with the flashlight on)
• You want remote access from another device
• You need identifiable video evidence
• You're monitoring while away from home (pet cam, front door, etc.)
• You have two devices and reliable wifi

The camera approach is essentially a DIY security camera. It's good at being a camera.

When to use LiDAR

Use Alarmist (LiDAR-based detection) when:

• You're sleeping in the room with the lights off
• You need to detect motion without any visible light
• You want to avoid false alarms from light changes
• You have one phone and want a self-contained alarm
• You're in a hotel, Airbnb, or unfamiliar place and want an extra layer of security

The LiDAR approach is a motion alarm for dark rooms. It's not trying to be a security camera.

They solve different problems

The honest answer to "can my iPhone replace a security camera?" is: it depends on what you're replacing.

If you want a daytime video feed you can watch remotely, a camera app on an old iPhone does the job. That's a solved problem.

If you want to know whether someone enters a dark room while you're sleeping in it, the camera approach fails at the most critical moment. LiDAR was built for exactly this scenario.

Cameras are the default answer for security. But the default answer doesn't work when the lights are off.

I built Alarmist because I wanted the second thing. I was sleeping in hotels and Airbnbs and wanted one more layer of awareness at night. Camera apps couldn't help because the room was dark. The LiDAR sensor on my iPhone could.

If you want to try it, Alarmist is on the App Store for iPhone 12 Pro and newer. You can preview what the LiDAR sensor sees in your room before committing.