hot mike

informal A microphone that is still recording or transmitting audio without the knowledge of someone within its range. The politician launched into a poisonous invective against immigrants and minorities after the cameras turned off, not aware of the hot mike broadcasting his every word to the whole world. Did you hear about the morning show host who was caught on a hot mike calling his co-host "dumb as a box of rocks"? A: "What's the latest controversy?" B: "Well, a hot mike backstage picked up someone making some pretty misogynistic comments."