Small Size Alarm: Compact design, smaller than most door window alarms. DIY installation, just peel & stick. It is easy to mount this alarm on any type of doors and windows, swing doors, rolling doors, sliding doors, etc.Loud anti-theft alarm: In constant alarm mode, once triggered, the continuous alarm will be a great deterrent for thieves and intruders. In doorbell mode, a loud sound will be an effective and quick alert when your children or pets sneak out of the house.4 working modes: general alarm, constant alarm, door closing alert. doorbell mode. Simply flip the side switch up and down to set the modes. Each mode corresponds to a different tone. Please refer to the product image for more details.Ideal for: Not only suitable for all types of doors and windows, but also for drawers, filing cabinets, safes, garage, camping -car, office, warehouse, store, etc.Low battery indication: Powered by 3 x LR44 batteries. Low battery consumption and long standby time. It will sound "Du Du" every half hour when the alarm is in low battery status.Description of principle:This alarm is an open window door alarm.The installation distance between the host and the magnetic bar should be less than 1cm.If the door/window is opened, the host and the magnetic bar will separate, the alarm will be triggered once the distance exceeds 1cm.Installation Instructions1) Attach double-sided tape to the back of the alarm and the magnetic bar, then stick them separately on the 2 sides of the seam of the door or window.2) Make sure the V-line of the 2 parts is aligned, make sure the distance between them should be less than 1cm.4 working modes:1) General alarm: the alarm sounds if the door is opened, the alarm sound stops if the door is closed. How to set: Flip the switch up. The quick sound is "Di-Di"2) Constant alarm: Constant alarm even door closed. How to set: Flip the switch up, down, up. The prompt sound is "Di......"3) Door close alert: sound "Di..Di..Di.." when the door is opened, it will s will stop when the door is opened. How to set: Flip the switch up, down, up, down, up. The quick sound is "Di-Di-Di"4) Doorbell: ring "DingDong" if the door opens. How to set: Flip the switch up, down, up, down, up, down, up. The rapid sound is "DingDong"Alarm dimensions: 56x30x17 mmMagnetic bar dimensions: 35x10x10 mmPower supply for alarm: 3 LR44 batteries (included)What you will get: 4 Pack of alarms