T40 RATTLER™ is a low-cost, maintenance-free single gas monitor designed to protect personnel from dangerous hydrogen sulfide or carbon monoxide gas exposure in the most extreme conditions. Despite its compact size, the T40 Rattler includes features usually found only in larger multi-gas monitors including a large, liquid crystal display (LCD), internal vibrating alarm, audible/visual alarms and simple push-button operation. The monitor continuously displays ambient carbon monoxide or hydrogen sulfide readings in PPM and will alert the user when gas concentrations exceed the preset low or high levels. Added features include adjustable alarm setpoints, calibration gas values, and choice of text-only display selected by the user through a simple, push-button routine. The T40 Rattler also has a peak/hold feature to show the highest reading during a shift and includes a patented flip-cap calibration adapter for quick and simple calibration. The T40 RATTLER operates for up to 1500 hours on a single AA battery (included) and is covered by a two-year warranty from the date of manufacture.