So I found my little “Taiwan Telephone Pickup” that I had bought at Radio Shack in the 1990’s, an induction microphone at the end of a rubber sucker that you’d suction onto an oldschool telephone handset when you wanted to record a call. No respectable Crank Yanker would be without one back then, but being a very special-use microphone, it kinda floats around looking for a place to live in a recording kit. While I had it in hand, I added it to my current field recording kit – a Lowepro belt camera bag containing everything I need to make good field recordings on the go. 
But what can you do with an induction coil mic other than record phone calls? Well, I saw a Hainbach video some time ago where he goes around making field recordings with a very high-sensitivity EMF induction mic, recording the ambient electromagnetic spectrum around him. While not anywhere near as sensitive as the wonderbox that Hainbach demonstrates below, a telephone handset induction mic works on the same principle and can pick up EMF spectrum at close ranges.
For this recording I fed the Telephone mic into my Sony ICD-BX140 voice recorder. It’s mono only, so the mono induction mic gave it a good signal. Good enough for the first test. The recording is of me waving the induction mic close to the stuff on my desk, including monitors, computers, a WiFi router to then moving over to the IBM Composer and flipping it on and running the mic around it. Then there’s the mic placed pretty close to the exposed CPU of the PiHole, and finally the faint hiss of very strong polarized magnets being held close in both attractive and repellent orientations. 
The IC recorder worked fine, but this experiment won’t be complete unless I use the Marantz PMD-201 and its input specifically for this sort of induction telephone mic. I think it’s got a preamp built in. I can also play with tape speeds then. (: 
Currently in the eyeholes: 
My pop has a microphone like that; He uses it to get a direct recording from his acoustic guitars!
You should play around with it – listen to all the EM around you :D
I had a few of those microphones since high school. I tried sticking them to almost anything, especially the utility poles since some audibly hummed and the mic. would pick up transformer hum from those we could not hear with our ears.
Check the TEL input on the PMD. If I recall it will work fine for any 500ohm or 600 ohm input. I forget if it was lo or hi level. (I need to check mine).
Remember the Radio Shack Zone microphones that looked like the Crown PZM 30s?
Yep, I have 2 of those Radio Shack PZMs, I use them for wide-field stereo separation recording. If Rat Shack sold it in the 80’s/90’s, then I bought it. (: