Gas concentration (ammonia, carbon monoxide, chlorine, chlorine dioxide, hydrogen cyanide, hydrogen sulfide, nitrogen dioxide, phosphine and sulfur dioxide) or percent oxygen displayed on a large, clear, backlit LCD. Automatically records the last 50 alarm/test events while simultaneously recording peak gas readings or low O2 readings every three minutes in a periodic data log. User can read data or change alarm set points by connecting unit to MSA Link via built-in IR communication port. Adjustable alarm set points. No-miss quad alarm system includes bright flashing LEDs, piercing audible alarm, LCD notification and an internal vibrating alarm. Rubberized armor housing and one-button operation for maximum durability and simplicity. Easy alarm check, bump check, fresh air zero and calibration. Easily replaceable batteries and sensors.