Capacitor charge, and no, night vision goggles don’t actually make that noise. But that sound effect has been burned into the public consciousness thanks to Hollywood and video games, so they have to put it in there otherwise people wouldn’t make the right association. It’s like shooting a gun with a silencer/suppressor screwed on the barrel being a complete shock when you hear it for the first time. You expect that quiet, *”phewt!”* sound, only to hear a gunshot, just a little quieter (but still loud as hell).
Latest Answers