Modern cars have a transponder imbedded in the top of the key (or key like device); hiding inside the plastic “head”. The car has a receiver inside the car that is asking for the identity of the key. The key sends a numerical signature back, and if the vehicle recognizes the right information it allows the car to start. Mechanical metal keys without this technology only allow a few thousand key possibilities. With this technology the number of different keys can reach into the billions, thus never having your car accidentally start with someone elses key. Additionally if a bad guy forces the ignition over to the start position, the car still won’t start because the vehicle does not see the elctronic signature it is looking for. While a spare key doesn’t cost two bucks anymore there is an upside; your car is a lot less vulnerable to theft because of this technology.