H-400 - LPG are flammable domestic gas leakage detectors. When flammable gas is present in concentrations higher than the dangerous threshold alarm level is activated. Red indicator bums and buzzer is turned on. Relay output can be used to close gas pipe electro valve.
Read manufacturer instruction manual, manual contains important safety information about the installation and operation of the detector. If the detector is in FAULT (yellow light) it must not be used any more, and should be replaced.