Two oxygen alarms can be set: CAUTION (20% oxygen) and DANGER (19.5% oxygen). Both alarm set points are factory set internally to prevent tampering or resetting by unauthorized personnel. When an insufficient oxygen concentration triggers an alarm, both the red panel light and an audible enunciator are energized. The alarms remain energized until the oxygen concentration has been elevated above the trigger point.

Calibration
A battery test push button is provided to visually check conditions of the batteries. Periodic calibration can be quickly and easily accomplished with the calibration adapter and a locking calibration control. The Model 335 uses a patented microfuel cell oxygen sensor which provides a linear output that is proportional to oxygen concentration. The sensor responds to even the slightest change in concentration within a few seconds. Its sealed electro chemical design is completely maintenance free. At the end of its useful life, the sensor is disposed of like a flashlight battery.