Sperian Biosystems ToxiLtd™ Monitors feature internal lithium batteries for up to two years of operation. Readouts consist of life remaining and current gas readings during alarm and 24-hour maximum. Low- and high-audible alarm alerts gas detection. Sperian Biosystems ToxiPro™ Monitors feature replaceable lithium batteries for up to 9000 hours of operation. Readouts consist of current, max, STEL and TWA gas readings and time. Low-, high-, STEL- and TWA-audible and visual alarms notify gas detection.