The engine immobilizer is a state-of-the-art anti-theft system. When you insert your key into the ignition switch or bring a Smart Key fob into the vehicle, the key transmits an electronic code to the vehicle. The engine will only start if the code in the transponder chip inside the key or Smart Key fob matches the code in the vehicle's immobilizer. Because the transponder chip is embedded in the key or Smart Key fob, it can be costly to replace. If you lose a key or Smart Key fob, your Toyota dealership can help.