The DW40 is a new Door/Window sensor from 2GIG with a handy local bypass feature allowing you to open the door or window without disarming the system, and the sensor is immediately re-armed as soon as it closes. Add to that its extremely compact size. If you would like to use the sensor on a window, but do not have glass break sensors and don’t want someone to be able to bypass the sensor by breaking in from the outside, that feature can be easily disabled.