As soon as the wireless sensors detect an alarm and transmit it to the solar-powered alarm system, it emits a loud siren of up to 110 dB and simultaneously activates the warning light to alert neighbors and deter intruders! The 5-piece starter set includes: - 1 x door and window sensor - 1 x PIR motion detector - 2 x remote controls for keychain. Expandable by up to 40 sensors. The outdoor siren can be wirelessly connected to the XMD-4400.pro or various wireless sensors - even via cable depending on the accessories! On the back of the solar alarm system, there is a protective switch that is activated if an intruder attempts to remove the device from the wall.