A transponder keys contain a chip deactivates a motor vehicle immobilizer when the car key is used to start the engine. The majority of keys to vehicles built just after 1995 include transponder chips. 
When the vehicle key turned in the ignition, the engine control unit (ECU) on the vehicle sends an electronic message to the core, and it will let the car to start only provided it receives the right message back. So even for a simple car key without any buttons, the key must be cut accurately to switch the locks and also programmed appropriately to deactivate the immobilizer. Car keys with chips can be processed by individual programmers using by a professional locksmith.
The Reason That Automotive Manufacturers Use Transponder Keys?
They are used to prevent the vehicle from being hot wired. The car will not even start if the device at the switch does not detect the low-level indicator through the key. If a copied key used without the proper signal, the vehicle will not start. When someone tries to hotwire the car, the car will not start because there is no sign coming from the key.
How Can You Tell If your vehicle Come With A Transponder Key?
In most situations, the plastic part of the key is going to be thicker than a key without a transponder. But it is not always the situation, but it is a good indication. One more test is to roll up the plastic part of the key with multiple layers of tin aluminum foil to then try to start the car. In case it does not start, there is a transponder there. There are a few exceptions to this guideline, but not many.
An additional indication that you have a transponder key is if it is expensive. Call your locksmith your VIN and inquire how much a replacement key will cost. In case it is a couple of bucks, possibilities are strong that it is undoubtedly not a transponder key. If it is over $100 or sometimes over $300, you can be sure that a transponder is present! Again, there are some exemptions, but not many.