Doppler Radar Motion Sensors - anyone used one

There seem to be a lot of devices like

on eBay. ( Search for Doppler Radar sensor ). Prices in the 7-12 USD range.

Anyone used one of these gadgets ?

Those are the radar modules without comparators. It is useless.... until you build a radar detection circuit with comparators.

You should use the radar modules with a sensitivity pot on the back side. Those have a digital output if motion is detected.