How Does a Remote Keyless Entry System Work?

Radio Signals

Remote keyless entry systems work by sending a radio signal from a handheld device to a receiver (sometimes a receiver is actually a computer system inside of an automobile). The receiver can be inside your car, garage or any other device programmed to recognize the signal sent by the remote keyless entry device. Most common types of remote keyless entry devices are fobs. Fobs are little contraptions that fit on your keychain.

Remote keyless entry systems used for cars

The programming behind the remote keyless entry system is usually in the car itself. The handheld fob is simply a circuit board containing a chip and battery housed in a small chassis of plastic (either built into the ignition key or on a separate, handheld device that attaches to a keychain). When a button on the fob is pressed, a small rubber pointer touches a spot on the circuit board inside of the fob chassis. This action activates the signal, which is sent to the car's computer. The circuit board inside your fob has a controller chip and a transmitter soldered on the circuit. The chip contains the code that the transmitter sends out to a receiver in your car.
A remote keyless entry system can be used to start the engine of an automobile, open the car's windows, pop the trunk, lock/unlock car doors and activate/deactivate an alarm. Some of the more advanced fob designs include a panic button. The panic button will stop an alarm when it goes off by accident and allow the driver to insert the key into the ignition. Advanced fobs can start the car engine without having to insert a key into the ignition.

Controllers and receivers

A controller can be clipped to the inside of your car's sun visor for opening and closing your garage door. The garage door opener (inside the garage) receives a signal from the controller when the button on the controller is pressed. The signal is a radio wave that carries a code from the controller to the receiver. Both the controller and the receiver are tuned to the same frequency. There are two codes that are transmitted from the controller to the receiver. One code identifies the controller to the receiver (using a 40-bit code). The other code is a command to open or close a garage door. In the case of an automobile, the command might be to open a door, pop the truck or even start the ignition. When the signal is sent from the controller to the receiver, the two devices generate a code by using a random number generator. The random number generator is the same for the controller and receiver. If another code is sent to the receiver by someone else's controller, the receiver will not respond.

Resources

• Buy a remote keyless entry system kit for your car or truck

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