How Does Transponder Car Key Work?


Transponder keys were developed during World War II for fighter planes and the word is derived from the combination of transmitter + responder. Transponder keys are specially designed handheld keys that transmit a radio signal to the vehicle’s remote receiver and used to unlock and start vehicles. The vehicle’s motor-receiver reads this special radio frequency with a designated, distinct digital identity code to lock or unlock the vehicle and it also starts the vehicle’s ignition system.

The type of transponder keys used in vehicles is called magnetic coupled transponder systems. Magnetic coupled transponder systems do not require constant electricity or a power source to operate. They operate in the frequency range area of 125 kHz. Magnetic coupled transponders are very range-limited and generally operate in the range of 1 cm to 100 cm.

Transponder keys are also known as chip keys and are a part of a remote keyless system used in vehicles. Each transponder key is programmed for a specific vehicle.

How Does it Work?

Transponder keys consist of a small microchip which has a unique serial number known as an electronic digital identity code. The digital identity code was set during its initial programming at the time of making the key. When an individual wants to unlock or start a car, he presses the transponder key and the chip inside the key, sends a special request (digital identity code) to the car. The engine of the car matches and validates the digital identity code and turn off the vehicle engine immobilizer to start the engine. If the car fails to validate the digital identity code/serial number, it will remain locked and immobilized.

In summary, Transponder key transmits a specific digital identity code to the vehicle engine. The vehicle engine responds back to the key with a validated key code. The key matches the key code, and it allows the car to start.

Advantages and Disadvantages of Transponder Keys


  • Most secure lock system for a vehicle
  • Duplication or bypassing transponder key is almost difficult
  • Keys can be used only to unlock car doors
  • Even if someone opens your car doors, engine won’t start


  • If you lose the original key, there is no way you can start your car
    (in such case, you need to contact your car dealer only)
  • Replacement of transponder car keys are very expensive
  • The range of key-frequency is limited
  • You need to be closer to your car to use transponder key
  • One can still open your car doors without original transponder key