I watched a small segment about this on TV the other day.
What they do is is lay in wait for a person to arrive home, switch on a jammer and the electronics can't pick up any signal from all the noise, the victim gets out and proceeds indoors the thief then jumps into the car, does what he needs, plants a GPS and waits.
The thief then tracks the vehicle or (going by what i remember) gain access to the car some other way (once inside the car)
https://www.youtube.com/watch?v=uD80a1rizLs