Open the battery cover, and remove black strip so that battery polarity can get continuation for power . close the battery cover Fix the main unit which has on-off switch at the side of the door & window. Attach the bar magnet to door frame/window frame with the arrow aligning with the reference line of the main unit. Switch to ”ON” position of the main unit so as to be in alert state, it will give an 110dB alarm if the magnetic senor has been separated from the alarm device when someone opens the door/window. Please turn off the switch when you don’t need. Remove the batteries to prolong the lifetime of the product/batteries if it will be set aside for a long time.