the higher end aftermarket remote start systems. change codes each time you use it. if its a two way remote meaning the car and remote send signal back and forth. this is what's on my car. Its made by clarion. anyway if the remote is away from the car for an extended period of time. you may have to press the button a couple of times. for system and remote to sync back up. and as far as extra remotes most systems allow up to five remotes. but they have to be programmed by a install shop. they have a machine that does it.