What Are Transponder Keys?

When you are looking at new cars to buy, the dealership may tell you that the car you want comes with a transponder key. You may not be sure what a transponder key is. It kind of sounds like something out of a science fiction story. However, they are quite common in cars, and not science fiction at all. 

Engine Immobilizer

The engine immobilizer in your car is a part that will not let your car start unless the immobilizing unit gets a particular code. Without that specific code, the immobilizer thinks that your car is being stolen and will lock up. It used to be used primarily in anti-theft systems but is becoming more and more common in all cars. 


Transponder is a mashup of two words, transmitter and responder. What a transponder is, when it comes to your car key, is a tiny chip that uses a radio frequency to broadcast a a code that is unique to your car. 

Transponder Keys

Transponder keys have this little chip inside them, usually under a thick plastic case at the top of your key. The plastic does nothing to inhibit the microchip's broadcast. What happens is that when you put the key into the ignition and turn it, that chip broadcasts the code. The immobilizer, which has a receiver in it, picks up that code and disengages. That allows your car to start. This process is nearly instantaneous, so you don't notice any difference in starting time from any other car. 

Benefits of Transponder Keys

The biggest benefit of using a transponder key is that it makes your car harder to steal. A thief would have a very hard time stealing your car without having your key. There are some bypass units that the thief could us, but the average thief isn't likely to carry the unit around. 

Drawbacks of Transponder Keys

One drawback to needing a transponder key for your car is that if you lose your key, you can't start your car. That's why it is a good idea to make sure that you have more than one key, just to make sure you are covered. Getting a new key cut isn't easy, nor is it inexpensive. The key has to be programmed with your car's code. That is something that you need a specialist for, like a locksmith such as Advance Lock & Key or your dealership. 

Knowing what a transponder key is can help you decide if you want to buy a car that uses this technology.