The POLI MP400 is a basic 4-gas detector for worker safety in hazardous locations, with sensors for oxygen (O2), combustibles (LEL), carbon monoxide (CO) and hydrogen sulfide (H2S). The MP400 is designed to be extremely rugged with a robust housing and gas sampling by diffusion for no moving parts. The simple, 2-button operation results in ultimate ease of use and significantly reduced time spent training the user. The rechargeable Li-ion battery pack lasts 16 hours or more in typical use, and the unique Man-Down alarm feature notifies nearby workers if the user becomes incapacitated.