Abstract: An intrusion detection device which has an optically extended field of view substantially greater than 180 degrees is disclosed. The intrusion detection device includes a radiation sensor and an optical system for concentrating radiation onto the sensor from each of a plurality of discrete fields of view extending over a predetermined arc greater than 180 degrees. A lens system has a plurality of segments each with its own field of view. Reflectors within the field of view of each of a plurality of the lens segments are oriented to gather radiation from a predetermined field of view outside the field of view of the lens system and to reflect the gathered radiation onto the associated lens segment to be concentrated onto the sensor.