1. A system comprising: a passive infrared (PIR) sensor configured to detect infrared radiation in a monitored area; a lens system including a plurality of lenslets, the plurality of lenslets encoded to create a mask area within a field of view of the monitored area; a reflective element configured to focus the detected infrared radiation in the monitored area onto the PIR sensor; and a processor configured to: detect a moving object in the monitored area; initiate movement of the reflective element; generating an object signature over time based on the detected IR focused onto the PIR sensor as the reflective element moves; and determining a size and location of the object based on the object signature.