system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: In reading about NSA PRISM, I've seen multiple statements about how cellphones can monitor you even when powered off. How is this possible? Does this mean that cellphones are never really "Off"?
gpt
Yes, provided they have a warrant to do so, the FBI can remotely activate the microphone and monitor you.  This came to light during the federal trial against John Gotti and the Gambino crime family.  To make the gathered evidence admissible in court, they had to display the warrants and explain how the gathering took place.  If you would like to research more about it (free of paranoid conspiracy theory) that's a really good starting point.