A:
I use it all the time great time saver and a great diagnostic tool. it lights up when it senses a magnetic field. ( FLUX ) ( ie ) energized coil in a relay or energized coil in a solenoid valve. I have had mine for years.
However very important, do not store anywhere near a magnet. it is very sensitive and will light near a magnet. Draining the internal battery that unfortunately is NOT replaceable a draw back on on my model maybe the newer ones allow for a battery change.
Answered on 3/6/2014 by Abe Barta from Holyoke Massachusetts