A motion detection system comprising: a focusing lens arranged to focus infrared radiation; a variably positionable optical attenuator arranged for variable positioning thereof opposite said focusing lens and operable for variably attenuating at least a portion of said infrared radiation focused by said focusing lens , at least one of an extent of said variably attenuated portion of said focused infrared radiation and a magnitude of said variable attenuation being dependent on at least one of a position of said variably positionable optical attenuator opposite said focusing lens and a set of physical characteristics of said variably positionable optical attenuator ; a PIR sensor positioned opposite said focusing lens and opposite said variably positionable optical attenuator , said PIR sensor being operable for sensing at least part of said focused infrared radiation focused by said focusing lens and at least part of said attenuated infrared radiation attenuated by said variably positionable optical attenuator ; and a human motion detection indication generator communicating with said PIR sensor and operable: for ascertaining whether an intensity of infrared radiation sensed by said PIR sensor is above a human-generated infrared radiation detection threshold; and responsive to ascertaining that said intensity of infrared radiation sensed by said PIR sensor is above said human-generated infrared radiation detection threshold, for generating an indication of detection of human motion, characterized in that positioning of said variably positionable optical attenuator opposite said focusing lens is achieved automatically by a motorized position controller . a focusing lens arranged to focus infrared radiation; a variably positionable optical attenuator arranged for variable positioning thereof opposite said focusing lens and operable for variably attenuating at least a portion of said infrared radiation focused by said focusing lens , at least one of an extent of said variably attenuated portion of said focused infrared radiation and a magnitude of said variable attenuation being dependent on at least one of a position of said variably positionable optical attenuator opposite said focusing lens and a set of physical characteristics of said variably positionable optical attenuator ; a PIR sensor positioned opposite said focusing lens and opposite said variably positionable optical attenuator , said PIR sensor being operable for sensing at least part of said focused infrared radiation focused by said focusing lens and at least part of said attenuated infrared radiation attenuated by said variably positionable optical attenuator ; and a human motion detection indication generator communicating with said PIR sensor and operable: for ascertaining whether an intensity of infrared radiation sensed by said PIR sensor is above a human-generated infrared radiation detection threshold; and responsive to ascertaining that said intensity of infrared radiation sensed by said PIR sensor is above said human-generated infrared radiation detection threshold, for generating an indication of detection of human motion, characterized in that positioning of said variably positionable optical attenuator opposite said focusing lens is achieved automatically by a motorized position controller . <EOS>