Auto Questions: How Remote Entry Works

Remote entry devices have improved greatly through the years and will continue to improve with technological advances.

Most new cars these days come with a remote entry device on a key chain. These remote entry devices also have the owner of the car pondering several questions such as what really happens when pushing the buttons, how can this device unlock the door from various distances and of course, how secure is this device if everyone has one? The answers to these questions lie with the remote entry devices themselves. There are two very common ones nowadays. They are the one that is one the key chain that is responsible for the locks on the car and one that fits on the sun visor of the car that opens a garage door. Home security systems also come with one, but these devices are not very common yet.

The first two mentioned the remote entry device on a key chain and the one used to open the garage door are actually small radio transmitters. When a button is pushed on the device a transmitter is turned on and a code is sent to the receiver. This receiver is either in the car or in the garage, depending on the remote entry device that is being used. The receiver located in the car or garage is tuned to the frequency that the transmitter is using, which is usually 300 or 400 MHz.

The very first garage door openers sent out a single signal and the garage door responded by opening or closing. As time progressed and the device became more popular, this system became very troubled because everyone who had a garage door opener could open other people's garage doors because they all used the same frequency. In the 1970's garage door openers were being manufactured with controller chips and DIP switches. DIP switches contain eight tiny switches arranged in a small package and soldered to a circuit board and are then placed inside the transmitter. The operator could now control the code that was sent by the transmitter, meaning that the garage door would only open if the receivers DIP switch was set to the same pattern as the transmitters. Even this was soon not enough security because the eight DIP switches only provided 256 possible combinations and could be figured out if someone was inclined to do so. Today's remote entry transmitters are a lot more sophisticated than these were and security is a big issue that has been improved upon. Modern controllers have a controller chip that uses a hopping or rolling code to provide this improved security and the mount of possible codes with this system is about 1 trillion.



The transmitter's controller chip holds the 40-bit code in a memory location and when a button is pushed on the remote entry device, the 40-bit code along with a function code is sent to the car, telling it what the command is, such as lock the doors, unlock the doors, etc. The receiver's controller chip also holds the 40-bit code in a memory location and if it gets the correct code, it performs the requested command. If the code is not correct, nothing happens. Both the transmitter and the receiver use pseudo random number generator for security purposes. The transmitter sends a 40-bit code, the pseudo-random number generator develops a new code and stores it in memory. When the receiver receives the correct code, it will use the same pseudo-random number generator to develop its new code and this synchronizes the transmitter and the receiver.

Remote entry devices have improved greatly through the years and will continue to improve with technological advances.

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