I did not know how to phrase it, but What the scan would do is you would hit a key and a notice would appear that your visor is scanning. then after about a minute it would display allies and enemies in the area of land you just scanned it to a predetermined distance. It would help distinguish friends and foes on dark maps, and areas with heavy vegetation.
No, he wants you to stand still for a minute to get a reading. Basically a tool for the camping snipers out there.