Abstract: A single FM/CW radar antenna and accompanying electronics are positioned within a space that is to be guarded. A moving object within the space under surveillance produces a doppler frequency shift in the echo return signal which return signal is, in turn, analyzed for signal content. Through FM and range gating the return signal analysis is selectively adjustable for moving target size and range such that moving targets of below minimum size and/or beyond maximum range are not detected as hostile objects while moving targets of or above minimum size and/or at or within maximum range are detected as hostile objects. Range gating is selectively adjustable to produce an alarm signal by selected size hostile objects within a predetermined range of detection, e.g.