A system is disclosed for determining the size and location of an object in a monitored area. The system includes a passive infrared sensor (PIR) 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 the monitored area, a reflective element configured to focus the infrared radiation in the monitored area onto the PIR sensor, and a processor. The processor is configured to detect a moving object in the monitored area, initiate the movement of the reflective element, generating an object signature over time as the reflective element is moved, and the size and location of the object is determined based on the object signature.