Door alarms go off 90dB loud sound to alert you when the window or door is open. Alarm loud enough to detect entry, prevent kids teenagers and babies from sneaking out the house, protecting your home or office whether you are in or out. No drilling, no wiring needed No screws needed Easily mounted by adhesive, tape it on the window or door then all is done (Notice: Please make sure the gap between the alarm and the magnet part is within 5mm/0.2in). Set up a simple home security system in minutes in an inexpensive way. Open the battery compartment and remove the plastic slip; Stick the small unit of product onto door window frame with the arrow facing left; Stick the large unit of product onto door/window within 5mm distance from the small unit with the On/Off switch facing left; Slide On/Off button to turn on the alarm and test by opening the door/window. No wiring needed, powered by 3pcs 1.5V LR44 button batteries. Powered By Batteries, but NOT Included. Please replace batteries timely when in low battery in case of influencing normal alarm. Easy installment are ideal entry warning for homes, apartments, mobile homes, offices, hotel rooms, garages, and more.