A remote key is a type of car key that uses a remote to lock and unlock the doors of a vehicle, whereas a transponder key contains a small computer chip that communicates with the vehicle’s engine immobilizer. The transponder key transmits a unique signal to the immobilizer in the car, allowing the engine to start. While a remote key is primarily used to lock and unlock the car doors, a transponder key is required to start the engine. Some car keys combine both functions, with a remote for door entry and a transponder for engine ignition.