The w:Automatic Warning System (AWS) swicthes in the Bodmin and Wenford Railway's Class 108 DMU 52054 which are located beneath the secondman's seat in the driving cab. The AWS is a supplementary signalling device. Before each signal is reached the train passes over a large magnet which starts the AWS' timing sequence. If the signal is green then an electromagnet next to the magnet cancels the sequence, otherwise the driver must acknowledge the danger (indicated in the cab by a horn and a yellow and black sign) by pressing a button. If they fail to do this the brakes will be applied automatically. The main switch allows the driver to identify which cab is at the front of the train.