Features: Authentic glass reed switch, super good quality, by no means comparable to junk with only two pieces of iron. Can sound an alarm when a burglar pushes a door or window. Inexpensive, easy to install and use. Scope of application: doors and for windows in a wide range of places such as homes, shops, factories, warehouses, etc. Installation method:1. Fix the host on the door/window with double-sided tape,2. Glue another bar door magnet to the door frame along the prompt line of the host in a straight line.3. When checking the settings, turn the main switch to the "ON" position.4. Open the door and see if the siren sounds from the alarm. Specifications: Material:ABS Power Supply: 2 Aa Batteries ( Not Included) Alarm Sound: 90 Decibels Package Includes: 1 Piece Door Window Alarms note: Please allow 1-2cm errors due to manual measurement,pls make sure that you do not mind before you order. Due to the difference between different monitors, the picture may not reflect the actual color of the item. Notice:No battery, need to be provided by the customer.