A transponder key, by basic definition, is a device that transmits or accepts data from another device. In the case of a vehicle, the transponder key is usually found in the ignition key itself, which gives the car another level of security and allows drivers to access their cars through keyless entry. These keys can be loaded with more than a trillion unique codes.
Transponders got their start in World War II, when they were placed on Allied aircraft to allow radar to determine if they were friendly planes or not. Transponders were placed on the aircraft and programmed with a set code that radar would recognize. Transponders are still used in aviation, but the most recognized uses are in consumer areas, such as vehicle keys and toll tags.
By attaching a transponder to a device, you're determining that at some point you'll need to find that device. The transponder key either receives or emits a predetermined frequency that is only recognized by the device that is supposed to recognize it, such as radar or sonar. In the case of a transponder key for a vehicle, the chip emits a signal to a receiving device located behind the steering wheel. If the receiving device accepts the signal, the car either unlocks or starts, depending upon what the driver is trying to do.
The transponder is inserted in the vehicle key in the form of a computer chip. Many modern vehicles feature keys that have a keyless entry, where the ignition key sticks out of a large, square case. In that case it is the chip, usually no larger than the tip of a finger, that allows the driver access to the vehicle.
The transponder key may not work if the chip itself has been damaged in some way or is losing battery power. In this case, it may emit a signal that the antenna in the car will not recognize, and therefore will not allow access to the car or the engine. This is considered a safety device for the vehicle, as the engine will not work if the antenna receives an incorrect signal, making it a passive safety feature that impedes car thieves. Because the frequency is unique to the car and the key, the car shuts down if a non-programmed frequency is used.
If you lose your keys, it's important to get a new set from your dealer or a locksmith soon after you lose them. Many cars require their antenna and keys be reprogrammed before a new set of keys can be issued. Many vehicles are issued with two sets of keys to prevent having to reprogram. Some cars allow you to buy a blank transponder key and use it to start the car. The transponder programs while you drive and takes about 30 minutes.
