What do you call this gadget [description inside]?

Question

Its sort of a tracker, a spy gadget sort of thing. You attach a small microchip or whatever you call it on a person, so you can keep track of where they are. You have a small screen thingy that shows the location of the person the microchip is attached to by a dot or something.

What do you call this gadget?

Answer 1

an electronic trace ?#?

Answer 2

gps locater?