Since the early 1990s, BMW has included electronic microchips in car keys to help deter thieves. The cars will not start if the key does not transmit the correct electronic signals when it is placed in the ignition. It is important to have your BMW's replacement key correctly made and have the new microchip programmed by a professional, or the duplicate key may not work.
Take your existing key to an automotive locksmith or BMW dealership. The dealership may charge more for its services, depending on what kind of blank keys are used and the actual cost to replace the key.
Have the locksmith or dealership make and program a replacement microchipped key.
Test the key to make sure it works. Open the doors and start the car. Keys that are not correctly programmed sometimes still work to open car doors, but will not start the car.
You may be able to save money by ordering microchipped key blanks online.
Use caution when selecting a business to duplicate your car keys, as keys in the wrong people's possession can lead to car theft.