Although coded keys come in a variety of sizes and shapes, with some devoid of metal altogether, the vast majority of coded keys feature mechanical operation that is not unlike standard metal car keys. Whether the key features additional security options or not, its primary purpose is still to unlock the various locking mechanisms that keep the vehicle secure. To accomplish this task, the key's unique shape aligns with pins and tumblers inside the car's door and steering column locks. When the key is inserted and turned, the design of the key allows it to press against the various pins and tumblers inside the locking mechanism and move freely; a key with a different design will not turn within the lock because steel keyguards prevent movement of keys that do not precisely align with the functional pins and tumblers.
The feature that truly sets coded automotive keys apart from their mechanical cousins is a small transmitting device either visibly mounted somewhere on the key or embedded within the key body. This transponder--so named because it both transmits and responds--emits a weak electronic signal that can be picked up by electronic devices in the car's ignition system. If the transponder is not present, the electronic security devices prevent the car from starting even if the mechanical portion of the key aligns and turns properly. This security device can be highly effective at preventing auto theft, as the transponder is capable of generating millions of security codes that must be received and accepted by the vehicle's security system for ignition to occur.
Radio transmitters are becoming increasingly common in coded automotive keys. These transmitters allow the vehicle's owner to send a command to the vehicle from several yards away, and the vehicle may flash its lights, sound its horn, open a door or start in response. The wireless radio transmitters work in much the same way as the lower-powered transponders, except they use radio waves--coupled with a small, hidden radio antenna inside the car--to broadcast their signal over greater distances. Some auto manufacturers even use radio transmitters to replace physical keys altogether; these devices interact electronically with the vehicle's security system to identify the keyholder and allow the engine to start by pressing a button rather than turning a key.
