Each module/channel is a complete instrument in itself with its visual alarms & relay outputs, except for regulated power supply which is provided by the master power supply board. It has the corresponding detector of application specific type. The detector is mounted at the location of interest and senses the gas if any through diffusion. It responds to vapor or gas, toxic, explosive or smoke, with the proportionate change in electrical characteristics. This change is electronically amplified and used to operate the electronic switching circuits & relay contacts. Isolated relays with NO/NC contacts are provided for signaling alarm and malfunction conditions. Relay contacts could be typically used to actuate remote alarms, increase ventilation, shut off the gas supply, or shut down a process. A suction based sampling system being employed, the sensor’s detectors are of very sturdy construction, with weatherproof or ex-proof housings and are designed to serve for several years under normal operating conditions. When a sensor detects a concentration of gas or vapor above the first preset level, it actuates an ‘ON’ alarm LED. Further increase in concentration, other alarm LEDs will be progressively actuated. With this arrangement, the user can readily distinguish the area harboring a gas concentration and its levels.