Passive Infrared Technology. No worries about buying and changing non-recyclable AAA batteries frequently. It's with a magnetic strip for mounting in addition to double-sided adhesive pads for places with limited electricity access.
It works very well and goes for a long time before it needs charging - but the plastic casing needs a bit of cutting away, because it makes the USB C charging slot too small for any known USB plug - including the onen they suppky!