The detector is fitted with a temperature compensating metal oxide sensing element which provides alarm outputs at two gas concentrations. Depending on the Kidde controller used, up to four or eight gas detectors can be used on a single channel. An end of line device is installed at the end of each channel to allow continuous monitoring. The best mounting locations include the engine compartment, the fuel fill port, and the fuel cylinder exhaust port. A trace alarm typically provides the driver with a visual and audible warning which resets if the gas concentration reduces. If significant alarm is reached, the alarm signal is usually latched and vehicle emergency protocols initiated. This allows the vehicle to be stopped with passengers evacuated safely.