Abstract: An infrared radiation detector comprises a pyroelectric detector element in a hermetically sealed housing. The housing comprises a base and a cover. The cover has an aperture surrounded by an inwardly directed flange. A self-locating window capable of transmitting infrared radiation is fastened to the flange with adhesive to close the aperture. The window comprises a first portion which is adapted to fit within and which is located within the aperture. A second wider portion forms a peripheral shoulder which bears against the cover's flange. The second portion of the window is present outside the cover, giving a wide field of view.