Motion Detector used in the movie "Aliens pt II". Does it actually exist?

In the movie, Aliens (part 2) there was a team of Space Marines that had these motion detectors attached to the front of their rifles. Man I thought those were SO COOL. Does anyone here know if something like that actully exist? If so, are they made availiable to the general public?

Motion Sensors exist, and I imagine it wouldn’t be that hard to set one up to show the position and distance of moving objects realtive to the sensor.

Here ya go!

The ones in the flick were described as detecting “micro-changes in the air currents” or something like that. Dunno how feasible that is…