Micro III Single Gas Monitors Micro III Single Gas Monitors are extremely lightweight at less than 4 oz. and very portable, measuring 1.85" x 3.5" x 1". Available for CO, O2, and H2S, they feature three alarm points, an LED readout, a confidence light or beep, and a magnet switch. The Micro III Monitors turn on when a battery is installed, and the AA alkaline batteries can easily be replaced in the field. Calibration Kits for Micro III Monitors include 34L calibration gas, regulator and adapter.