Hidden discreetly within the frame of a door, the only visible part of the EV-DW4917 wireless recessed door/window contact once installed is the access cap (available in white or brown). Access caps are either flanged or non-flanged and allow for either a screw-mount or a press-fit installation. A flat head screwdriver is used to change the cap if needed or access the battery. Primarily designed for installation within a door, the transmitter can also be used within the frames of windows. The EV-DW4917 is built with reliable 433 MHz technology, is powered by a replaceable lithium battery and is compatible with all current DSC wireless receivers. The EV-DW4917 is designed to provide installers with flexibility during difficult installations. By having access caps flanged or nonflanged, installers are able to decide whether it's necessary to screw mount or press-fit an installation. Another feature of this installer friendly device is its replaceable lithium battery that provides uninterrupted supervised security for many years. Inconspicuous and Unobtrusive Barely discernable once installed, the EV-DW4917 is completely hidden when the door is closed. This is ideal for those customers who do not want to compromise the aesthetics of their decor.