The ProtonZM single-gas monitor offers two years continuous protection from H2S or CO with zero maintenance — no calibration or battery/sensor replacement needed. According to the manufacturer, the ProtonZM instrument is the only single-gas, zero maintenance detector that indicates required bump testing and displays peak value over the past 24-hour period and the product’s remaining life.Scott Health & Safety, www.scotthealthsafety.com, (800) 247-7257.