All smoke alarms have a TEST button. To test the unit, hold the TEST button down for anywhere between 2-5 seconds and you should hear a loud beep. If you don’t hear anything or the beep sounds weak it means the batteries need to be changed. Next, test the smoke alarm with real smoke. To do this, light a match and blow it out below the unit. It might take a few seconds but the alarm should go off. If it doesn’t, change the batteries and test again. If it still doesn’t work then the unit should be replaced.