4、ncentrationofcombustiblegasesintheenvironment,oncetheconcentrationexceedsthealarmlimitvaluecanbeaudibleandvisualalarmsignal,openventilationdevices,andcanalarmvolumeincreasesastheconcentrationincreases,whileremotealarm,intimetoplayasecurityrole.Keywords:SIM900A; MCU; Gas det