MAGNETIC: The alarms work thanks to the magnetism between the alarm transmitter and the magnet receiver. The 100 dB siren is triggered when an equipped door or window is opened (trigger spacing: more than 10 mm).^ EASY: The alarm sensor and the magnetic receiver are equipped with adhesive tape. No tools needed, you just need to stick them on a door frame.^ TECHNICAL DETAILS: Transmitter dimensions: 9 x 3 x 2 cm; magnet receiver: 5 x 1 x 1.5 cm | Batteries: 2x AAA 1.5V per alarm (included) | Volume: 100dB^ MANY USES: Increase the security of your front door, patio or balcony, your room or that of the children - the set of 4 alarms and receivers give you the choice.^ NOTE: Please make sure that your apartment or house has the right conditions for setting up the security system, without accidental triggering.