Wireless motion sensor such as infra-red and Doppler is commonly used for our home protection against intruder. Wideband or ultra-wideband (UWB) sensor has lately attracted considerable attention because it is expected to measure not only motion of an intruder but also the distance. This paper suggests a stepped-FM UWB sensor which can cover all the rooms of a house. UWB systems may cause unacceptable interference to existing wireless users of the same and nearby bands. Therefore interference mitigation technique called DAA (Detect-And-Avoid) device is required to be implemented for UWB users. Our suggested sensor provides inherent ability to coexist with other wireless systems without additional DAA device. This is because it can take any optional spectrum hole (non-activated within a portion of the wide radio spectrum) for the UWB transmission. The measurements had been conducted for various scenarios in a typical house with three-rooms and the results are presented.