MAGNETIC: The alarms work thanks to the magnetism between the alarm transmitter and the magnet receiver. The 90 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 (included) | Volume : 90dB MANY USES: Increase the security of your front door, terrace or balcony, your bedroom or the children&39;s room - the set of 4 alarms and receivers give you the choice. Uses: it can be installed on the doors and windows with switches. When the switch is turned on, if the doors and windows are opened, an audible alarm will sound. Turn on the alarm switch when you sleep at night or when you are not at home or in the office, which can be safe and anti-theft. White color Number of pieces delivered: 4 pieces NOTE: Please make sure that your apartment or house has the right conditions for setting up the security system, without accidental triggering.