Beams reflected, sweeping back and forth? (5)
I believe the answer is:
radar
This might be a double definition.
'beams reflected sweeping' is the first definition.
'radar' can be an answer for 'beams' (I've seen this before). I'm not certain of the 'reflected sweeping' bit.
'back and forth?' is the second definition.
Can you help me to learn more?
(Other definitions for radar that I've seen before include "System of detection by echoes" , "Early warning system" , "Range and direction finding equipment" , "Instrument to detect and track distant objects" , "Means of detecting and locating distant objects" .)