Analysis of information sources in references of the Wikipedia article "Wiretapping" in English language version.
The FBI appears to have begun using a novel form of electronic surveillance in criminal investigations: remotely activating a mobile phone's microphone and using it to eavesdrop on nearby conversations. […] Kaplan's opinion said that the eavesdropping technique "functioned whether the phone was powered on or off." Some handsets can't be fully powered down without removing the battery; for instance, some Nokia models will wake up when turned off if an alarm is set.