Factory security is rubbish!! Simple!!
The use of a 'scanner ' aka code grabber allows easy access into a car... A theif with these special scanners simply waits for a person to lock/unlock their car from a distance... once you press your keyfob the signal is picked up by the scanner and copied... once you've left your car the theif simply unlocks your car with the copied signal...
Dont know about other alarm systems, but Clifford use a scrambled code/ code hopper programme... everytime the keyfob is used a different code is used..