can you use a cell phone as a spy camera?

I heard that someone put acell phone in there x,s car and it was used as a stalking devise,is this true?If so could there be audeo also,where would they have hidden it?
Would anyone know where to get this software?And what it is named ?or who makes it.
Is there any way to block it or catch someone using it?PLEASE! I may now someone being stalked this way and he has been dangerous in past situations with this person.