AI Smarthome Technology9 June 20261 min read
Motion sensors were never the right idea
If the light goes out while you are reading, the sensor is not broken. It is answering the wrong question.
A passive infrared sensor detects change: something warm moved across its field of view. That is a fine proxy for occupancy in a corridor and a poor one in a room where people sit still. Everybody who has waved an arm at a ceiling from an armchair has met the limitation.
Millimetre-wave radar answers the question that was actually being asked. It detects that a body is present - breathing counts as movement at that wavelength - so the light stays on over the book and goes off when the room is genuinely empty rather than merely calm.
The second thing it brings is zones. A radar sensor can report which part of the room is occupied to within about half a metre, which is what makes "light the desk, not the whole room" a rule you can actually write. Pair it with an ambient light reading and the lamp stops switching on at noon.
The trade-offs are real and worth stating. Radar sensors cost more than PIR, they need mains or USB power rather than a coin cell, and a sensor that knows where people are in a room is a sensor whose data should stay in the house. Local processing is not a nicety here.
