The one I have used is:
Acousticom 2 Pocket-Sized EMF Meter 0.2-8.0GHz
This is not the professional, laboratory-grade type of instrument that I would normally like to use, but it seems to do a good enough job for searching for hot-spots. I posted a YouTube video using this device:
i have not yet felt that āinternal motor runningā sensation w/o the device, BUT i have felt a sense of calm over my body when sleeping with itā¦ a few times when it is quiet and I awaken w/the device running, I do feel this āblanketā of peace/calm over me. This is just running the a9 unit too.