Pictured at right is a four channel
FuelGuard system in a NEMA 4X
Enclosure with window. 
Four sensors are connected by cable
for installation in the vehicle.

A FuelGuard system consists of up to eight leak detection modules (4 shown here) each connected to a sensor located in a remote part of the vehicle.
Each sensor constantly watches for gas. When a sensor detects gas, it sends a signal to the leak detection module which compares the level of gas found to user-set limits. It has its own digital readout. The leak detection module sends its alarms to the common alarm module. Depending how the alarm module is wired the signal may be passed to the annunciator panel. The alarm module has relay outputs for each alarm level which can be interconnected to other vehicle systems (fire suppression or ignition interlock).