A passive infra-red detector including at least three sub-detectors, each sub-detector being operative to receive infra-red radiation from a corresponding one of at least three sub fields-of-view, each sub field-of-view being exclusively defined by an optical element which does not define any other sub...http://www.google.ca/patents/US7504633?utm_source=gb-gplus-sharePatent US7504633 - Passive infra-red detectors
