You can get little 5GHz doppler radar modules designed to operate a relay for automatic light switching: on the ones I have, you can disable the light sensor, so it will detect any motion. The sensitivity and 'on' period are also adjustable. They will 'see' through a wooden door quite easily, so can be mounted inside. They came installed in some Osram automatic LED luminaires. I have these set up in pairs, so a couple of the modules were surplus. I set up one to turn on the light in the front porch when someone approaches, though it occasionally gets triggered by by large vehicles (horse boxes!) passing in the road. The other one is in a box somewhere. I can't remember the manufacturer name though, it wasn't Osram.