"Nextel cell phones...were used by the FBI to listen in on nearby conversations... The eavesdropping technique "functioned whether the phone was powered on or off." Some handsets can't be fully powered down without removing the battery... "They can be remotely accessed and made to transmit room audio all the time...without having physical access to the phone."

A 2003 lawsuit revealed that the FBI was [also] able to surreptitiously turn on the built-in microphones in automotive systems like General Motors' OnStar to snoop on passengers' conversations. When FBI agents remotely activated the system and were listening in, passengers in the vehicle could not tell that their conversations were being monitored."

See: CNET News article (2006-12)