Your car's key fob could have hidden features that you never knew existed. Motorists may be able to personalise their driving experience with the press of a button on their car's key fob, thanks to a secret button that many of us knew nothing about. According to a car expert , there's a button on certain petrol and diesel car key fobs that will allow you to personalise a whole host of features including seat position and top speed - which will be remembered by the fob the next time it is used.