Why a light switch doesn't trigger it

Turning a lamp on, a cloud crossing the sun, or the camera's own auto-exposure adjusting all change nearly every pixel at once. OdinCam recognises these and ignores them, then catches its background model up to the new light level within about a second.

The test is not simply how much of the frame changed — someone standing close to the camera also covers most of it. What distinguishes a lighting change is that every part of the frame shifts by a similar amount, whereas an object changes the area it covers and leaves the rest alone.

When this happens the meter reads "lighting change — ignored", so you can tell the difference between the detector rejecting something and it not seeing anything.