As shown in FIG alarm by a gas-sensitive sensor element QM, buck rectifier and regulator circuits, integrated circuits KD28, speaker Y and other components. Gas-sensitive senso
r element QM is QM-N5 type. Buck regulator circuit by a transformer rectifier and B, the rectifier bridges D1 ~ D4, C1, C2, integrated voltage regulator 7806 and other components.In operation, the adjustment potentiometer W, so energized for 1 minute. When the air is clean, QM corresponding resistance value is large, the partial pressure of the small W, so that the KD28 reset the alarm does not occur. When flammable gas when in contact QM, QM corresponding resistance value is small, the pressure on the larger points W, so that the KD28 set, 3 feet high output speaker promoting work, an alarm signal. After the gas leaves the circuit will resume normal operation.