The most common failure mode for a home security camera is not hardware. It is the owner switching notifications off after a fortnight of being told about shadows. A camera whose alerts you ignore is not providing security.

Two ways cameras detect motion

Pixel-change detection compares consecutive video frames and triggers when enough of the image changes. It requires no extra hardware, which is why almost every cheap camera uses it. It cannot distinguish a person from anything else that changes the picture — and a great many things change the picture.

Passive infrared (PIR) uses a dedicated sensor that detects moving heat signatures. A human body at roughly 37°C moving across a cooler background produces a clear, distinctive signal. Light changes produce none at all.

What sets off a pixel-change camera

• Clouds moving across the sun, changing overall scene brightness
• Headlights sweeping across a wall through a window
• A television or monitor in frame
• Curtains or plants moving in a draught
• Insects and dust close to the lens — especially at night, when infrared LEDs light them up brilliantly
• The camera's own infrared switching between day and night mode

PIR ignores every one of these, because none of them is a moving heat source.

The battery consequence

On a battery camera this is not merely annoying. Every false trigger wakes the camera, records a clip, and transmits a notification. A camera rated for weeks of standby can be flattened in days by an over-sensitive sensor pointed at a curtain. The XCAM Nano's 45-day standby figure assumes the PIR sensor is genuinely idle most of the time — point it at a busy street and that number collapses.

Practical fixes

1. Reposition before adjusting settings. Getting the TV, the window or the swaying plant out of frame solves more than any sensitivity slider.
2. Use detection zones if your camera supports them, and mask the parts of the frame you do not care about.
3. Lower the sensitivity in stages and live with each setting for a day. Dropping it to minimum immediately usually means missing real events.
4. Watch for pets. PIR is much better than pixel detection here, but a large dog at close range still registers. Mounting slightly higher and angling down helps.
5. Clean the lens. A spider web or dust across the lens produces constant night-time triggers from IR reflection.

Choosing for this

If reliable notifications are the reason you are buying a camera, treat PIR as a requirement rather than a nice-to-have — it is the difference between a camera you trust and one you mute. Our buying guide covers the other specifications worth checking, and camera placement covers the positioning side.