I bought some $100 Radian muffs last year from a local store. They do the 'clip' thing, shutting off all sound for a couple seconds. After a while they started to develop a buzz that was distracting so I took them apart...
Seems the 'electronics' consist of a small metal cylinder with a tornado-looking spring in the middle. A strong sonic pulse would make the spring jiggle and hit the metal cylinder, cutting the sound.
They're somewhere in a landfill now.