A high quality gas detector detects different gases in a certain area, usually as part of a safety system. An industrial process can then be shut down. Certain gas detection equipment can also sound an alarm in an area where the leak is. This gives operators opportunity to escape. Gas detectors can be used to detect oxygen depletion, combustible, flammable and toxic gases. These devices are used widely in industry in a variety of locations i.e. oil rigs to monitor manufacture processes, and in emerging technologies. Alarms and flashing lights are sounded when dangerous levels of gas vapours are detected. Gas detection equipment measures a gas concentration against a calibration gas that acts as a reference point. In the early days of gas detection gas monitors detected a single gas, but a modern gas monitor can detect several toxic or combustible gases, or even combinations. Monitors are either portable or stationary / fixed devices. Portable gas detection equipment is usually battery operated.