That may well have been to provide power to passive listening devices.

https://en.wikipedia.org/wiki/The_Thing_(listening_device)

It’s amazing to think that it was invented by Theramin. Also:

Theremin created the Buran eavesdropping system. A precursor to the modern laser microphone, it worked by using a low-power infrared beam from a distance to detect sound vibrations in glass windows.

Theremin is one of the true geniuses, the list of inventions and fields is incredible.