Detecting very simple movements (a hand waving) usable on 8bits microcontroller
Those two are definitely ultrasonic transducers. One for Tx one for Rx. My guess is that only a hand wave close enough (because of the tilt angle) will trigger this. It could detect a simple echo, or might even do a doppler analysis to detect movements. More advanced method would be to use a "chirp" signal, but I doubt that is required here.