The user controls the remote start system via a tiny remote, not unlike the remotes many drivers have to activate and deactivate their car alarms. The remote sends a very specific signal to installed pieces of equipment inside the car. This frequency is generally encrypted, which prevents someone from figuring it out and sending an identical frequency and starting your car remotely without your authorization. When the starter receives the signal from the remote, it switches on all these systems. It allows the engine to start, which allows preset settings like heat to come on and begin to work. It also locks the doors, and typically blinks the lights for visual confirmation that it is working.
