We recently tried using a phone coil pickup on various bits of equipment. Coil pickups works by recieving and amplifying electro-magnetic fields which are generated by the circuitry inside electronic equipment whilst they are in use. This can lead to some interesting results, as we found when we used it on a printer/scanner and one of our iPhones!

We’ve got a recording of each, plus a few pics of the mics setup on the appliances.

This recording is the coil pickup mic used on the iPhone:



This recording is the coil pickup mic used on the printer/scanner:



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