A transponder is short for: transmitter + responder. The word was invented around 1944.

In basic terms a transponder is a miniaturized electronic chip that has what is called nonvolatile

memory. Nonvolatile memory is the type of memory that does not need constant energy for

retention. Along with that electronic chip is a set of windings, very fine wire coiled around a tube.

These windings look similar to the windings you would find in a electric motor.

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 manufacturer’s 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 125KHz. Since Magnetic Coupled

Transponders do not have their own power source they are very limited to range of communication

and generally operate in the range of 1cm to 15cm. 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 bow of a key.

The process of key identification is similar in most automotive transponder systems. Once

a key is inserted into the ignition lock and turned to one of the ‘on’ or ‘run’ positions, the induction

coil that is mounted around the ignition lock sends out an electromagnet field of energy. The

windings in the transponder chip absorb that energy and power the electronic chip to emit a

signal. The signal is usually an alphanumeric set of digits which is considered the Identification

Code. The induction coil reads the signal and sends it to some type of computer device to recognize

the signal. If the signal is recognized 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.

Transponders can be made into several different shapes and sizes and can be used in

many different types of applications such as: warehouse pallets, retail clothing, animal management,

and of course electronic automobile key identification.