MyCarKeys

How your car key works (transponder technology)

When the car key is turned in the ignition, the engine control unit (ECU) on the car sends an electronic message to the key, and it will allow the car to start only provided it receives the correct message back. So, even for a simple car key without any buttons, the key must be cut correctly to turn the locks, and also programmed correctly to disarm the immobiliser.

Car keys with transponder chips have to be programmed to your vehicle using specialist diagnostic equipment.

What is a Transponder?

A transponder is short for: transmitter + responder

The word transponder was first coined around 1945. In layman’s terms a transponder is a miniaturized electronic chip that has anon volatile memory. This is a type of memory that does not need a constant energy supply to retain its data. Along with that electronic chip is a very fine wire coiled around a tube. This is in effect like an aerial amplifying the data on the transponder chip when interrogated by the cars ECU (engine control unit)

There are two basic types of transponders. The first are the electric coupled transponder systems. Electric coupled transponder systems are not limited to small areas for transmission but can transmit messages or signals for different ranges of distance including several inches to miles, as used in satellites and airplanes. These systems require large amounts of constant electricity to operate. The second type is what automobile manufacturers are using and they are called magnetic coupled transponder systems. Magnetic coupled transponder systems are passive in nature. This means they do not require constant electricity and thus do not need a power source of their own. They operate in the frequency range area of 125 kHz. Since magnetic coupled transponders do not have their own power source they are very limited in range of communication and generally operate in the range of 1 cm to 15 cm. Since this is a radio frequency it can penetrate materials that would make the transponder not directly visible, such as the plastic or rubber in the head of a key.

The process of key identification is similar in most automotive transponder systems. Once a key is inserted into the ignition and turned to one of the 'on' or 'run' positions, the induction coil that is mounted around the ignition sends out an signal of energy. The aerial in the transponder chip receives the signal and power the electronic chip to emit a signal. The signal is usually an alphanumeric sequence which is considered the identification code. The induction coil reads the signal and sends it to some type of computer device to recognise the signal. If the signal is recognised as being already in the computer’s memory the signal is accepted and other electronic components in the vehicle are set into motion to allow the starting of the vehicle or the continuation of the engine running.

Immobiliser systems based on Transponders may not be as safe as they are considered to be. Some immobiliser systems tend to remember last key code for so long that they may even accept a non-transponder key even after a few minutes of taking out the original key from ignition.