Your vehicle may contain an anti-theft element without you even knowing it. Transponders are molded inside the head of the key where you would not notice it. It is termed a passive anti theft method, as the security requires no action by the vehicle operator.
Another type of "chip" key is the GM VATS, or PassKey II. This one has a visible resister pellet embedded in the blade.
Other forms of passive theft deterrent include MRD (a magnet embedded in the ignition cylinder that creates a measurable "Halls effect" when the proper key rotated in the lock), and MATS (a steel plate in the steering colomn). There is nothing special about the keys in these two setups, as they are mechanical obstacles to deters a forced ignition attempt.
Here is a list of vehicles equipped with a theft deterrent system.