Abstract: A passive infra-red detection apparatus is described, which comprises an infrared sensor array (16) mounted in a housing (10), and a focusing reflector system (20, 22) and focusing refractor (14) which focus infra-red radiation from different distance ranges onto the sensor array (16). The sensor array (16) comprises at least three sensing elements or groups of elements (16A, 16B, 16C) spaced apart transversely with respect to the lens axis of the focusing refractor (14). Thus in combination with a multiple reflector (20, 22) having at least three reflector surfaces and/or a multiple focusing refractor (14), the sensor array receives several different views spaced apart transversely thereby providing a wider viewing angle than the prior art construction. Thus, the present detector is more suited to use with a closed-circuit television (CCTV) surveillance system.