Did everyone spot it?
The Killing, Series 2, Episode 7, 17'30".
Raben's father-in-law tells him Special Branch are following him. Raben instantly takes something out of his pocket, fiddles with it and puts it back.
He was taking the battery out of his mobile phone – the only way to be (fairly) sure that it isn't being used to locate/track him.
Him. Or anyone else. You, for example. Your mobile phone is a voluntarily worn electronic tag. Your mobile phone, and mine, is an electronic ID card.