[genewitch]

They're like shooting muffs/cans, except they have a microphone on each side, batteries, and an amplifier. when it's off, they're regular hearing protection. When you turn them on, you can adjust the volume from "slightly lower than without the muffs on", to "actual volume", to "hear a cricket fart across the street". When a loud sound is detected - say, clapping, gunfire, hitting an anvil - it shuts off the amplifier.

As an aside, since your ears are not ringing / recovering from a very loud sound, and the amplifier turns back on very quickly, you can hear the reverberations, echos, and sympathetic resonances. It's quite cool.