1. A ranging device for monitoring a scene of interest, the ranging device comprising: a transmitter for transmitting pulses toward a scene of interest; a receiver generating pulse samples indicative of a content of the scene of interest based on returned pulses; and a target discriminator including a detector sample output for identifying changes in a scene of interest arising from at least one of a target entering said scene of interest, a target leaving said scene of interest, and a target moving in said scene of interest, based on short term high order statistical samples derived from said pulse samples in comparison with long term high order statistical samples derived from said pulse samples.