Transponder
Transponder is short for: transmitter + responder.

The word came into use 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.


                   (This information was borrowed from HowardKeys.com,
                        a supplier of transponder keys to locksmiths.)