Detailed Product Description HM-703-2 (wired):9V-24VD.C,auto-test for malfunction,Output:relay(N.C&N.O) and sound & flash alarm; wall mounted;Alarm level: 10% of Natural gas; HM-703L-2(wired,low consumption):9V-24VD.C.,auto-test malfunction,Alarm Output: relay output N.O./N.C and sound & flash alarm, low power consumption designed. Wall mounted;Alarm level: 10% of Natural gas;