Easy InstallationNo Need to use complicated tools when installation, just use 3M glue to install, firm and durable. The two arrows are opposite, the distance between the two compopents should be as close as possible, and the closest distance should not affect the opening/clsoing of the door or window.
Low Power warning: The sensor door need with TWO AA Batteries (not include). When the battery level is low, it will automatically push messages throuch APP to remind you to change battery, never worry about running out of battery.