Keeping in mind the upcoming Motion Detection Zones app, I’d suggest the Xioami Aqara Motion Sensor as a low-cost solution (as low as $12.50 each via AliExpress if you don’t mind waiting a couple weeks for China EMS -> USPS ePacket delivery.)
I am using them in tandem with a few other (more expensive) PIR devices, to keep costs down. They are tiny - only 1 1/16" diameter and 1 1/4" tall, with an equally small mounting bracket.
They only send motion detected messages with a hardware reset of 60 seconds, but the device handler I’ve shared takes care of automatically sending a motion inactive event at the time of your choosing. I’ve had great luck using them as PIR lighting triggers for me.
Lux is also reported, but only some milliseconds before or after the motion detected message (to save on battery usage), so I imagine setting up a rule that delays action on the motion trigger until lux can be evaluated might be the best way to deal with that.
Caveat Emptor: It being a “cheap” Chinese sensor intended to work specifically with their own ZigBee hub solution, I was skeptical myself, so I ordered one to do testing with, and now I have half a dozen with plans to get more.
