... and TWA alarm function for toxic gases l Power on self-test functionl Adjust high and low alarm levell ... diode Sound: 90 Db humming; when concentration increased, frequency increasesVibration: oscillator speed of 1300 r/minWorking VoltageDC3.6 ... industry, coal mine, papermaking, fire-fighting, municipal affairs, pharmacy, power plant, chemical industry, mine, tunnel, underground pipeline, etc.Product ...