MAGNETIC: The al work thanks to the magnetism between the alarm transmitter and the magnet receiver. The 100 dB siren is ed when an equipped door or window is opened ( 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: B^ MANY USES: the security of your front door, patio or balcony, your room or that of the children - the set of 4 al and receivers give you the choice.^ : Please make sure that your apartment or house has the right conditions for setting up the security system, without accidental ing.