sounds, sensors, stones
This is for a piezo contact mic that is powered off a field recorder’s plug-in-power supply. That is for small recorders like Olympus’s LS10, LS-5, LS14 series, which are typically unbalanced audio inputs, stereo on a 3.5mm jack, not for a P48 phantom power from a mixer or pro recorder 1 . You also get an opportunity to drink beer.
Batteries are a pain in field recording. One battery to rule ’em all is best in my book, the fewer things with a battery required to make a system work the better. The recorder generally has to have a battery, and Sony agreed with that many years ago, back in the days of Minidisc , and came up with plug in power (PiP). to eliminate the battery in the microphone. An electret mic doesn’t need much power so battery life is weeks not hours, but it has a switch you often forgot to switch off.