All BMW vehicles are equipped with an anti-theft mechanism. This means that these vehicles are protected from being started with a simple mechanical copy of the car key.
BMW E-series remote control keys are unusable, i.e. it is impossible to open them or replace the battery inside.
The BMW F and G series use keyless technology, but the remote controls contain replaceable batteries.

BMW keys programmed for one vehicle cannot be reprogrammed for another.
So if you have an old BMW key copied and programmed, you will save a lot of time and money should something happen to the original key.