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, just stick them on a door frame. TECHNICAL DETAILS: Transmitter dimensions: 9x3x2cm; magnet receiver: 5 x 1 x 1.5cm | Battery : 2x AAA 1.5V per alarm (This product does not include batteries)| Volume : 100dB MANY USES: Increase the security of your front door, patio or balcony, your bedroom or the children's room - the set of 4 alarms and receivers give you the choice. NOTE: Please make sure your apartment or house has the right conditions for the security system to be set up without accidental triggering. Please note that due to manual measurements and display differences, there may may be slight differences between individual products and photos.