The unit is supplied with the capability to measure four gases. Ultra-bright alarm lights and a powerful audible alarm, coupled with a periodic green flash and bleep, provide user confidence that monitoring is always in operation and alarms are never missed. Ranges covered: Oxygen 0-25% Methane 0-100% LEL Carbon Monoxide 3 to 500 ppm Hydrogen Sulphide 0.4 to 50.0 ppm Unit supplied with rechargeable battery pack and mains charger. Full certification is provided