The battery operated sensor consits of the main unit and a magnetic element. The main unit should be installed on the frame and the magnetic element is placed on the door or window. The mounting of the 2 elements can be done with screws or stickers.
In combination with additional devices of Z-Wave like a siren or motion sensors you can create your own alarm system which promises more safety. All you need is a combination of the mentioned sensors like the Door/Window Sensor and a Z-Wave Smart Home gateway.