Later systems replace the automatic air brake with an electrical wire which runs in a circle round the whole train and has to be kept energized to keep the brakes off. In the UK it is known as a "train wire". It is routed through various "governors" (switches operated by air pressure) which monitor critical components such as compressors, brake pipes and air reservoirs. Also if the train divides the wire will be broken, ensuring that all motors are switched off and both portions of the train have an immediate emergency brake application.