Allows us to see in the dark.
Fitted to most aircraft, ships and countries to detect nasty people, before they twat them back to obscurity.
Also on some missiles and guns to guide them onto targets.
It was invented in the '30s by the British, and used to great effect by the RAF during the Battle of Britain, detecting Luftwaffe raids and scrambling aircraft just in time.
Radar is now used for meteorology as well as detecting the fuzzywuzzys.
It works by sending out a radio wave and receiving the reflection of the signal, which gives a fairly accurate fix.