It looks like a rather cheap and nasty Gunn module as used in some alarm systems they were used in a similar way to PIRs and worked on the doppler principle at about 10GHz. We used to modify them to form the basis of amateur radio wideband 3cm microwave transceivers. They have gunn diode oscillator cavity with a mixer diode in front of the gunn, a reflected signal from a moving body is shifted from the base frequency (doppler shift) and when mixed with the base frequency gives a frequency proportional to the speed of the moving body (hence also used as base for radar speed detectors). Hope that helps.
Regards Dave