Their unwitting confessions are broadcast to the police via a hidden microphone and radio transmitter.

They discover in the basement a lamp which could serve as a decoy for a hidden microphone.

Instead, he convinces his superior to let him do a reportage using a hidden microphone to gauge people's reactions on being asked outlandish questions.

The scenes featuring the rhinos were filmed using special cameras while hidden microphones captured the rare communication.

All the rooms had been made acoustically efficient with carpets and curtains, and fitted with hidden microphones, which allowed us to record the prisoners' conversations on gramophone records.