A surveillance unit (1) comprises a support pole (3) and apparatus (5) mounted on the support pole (3) for housing surveillance cameras (6,7) and infrared heat detectors (8) in a controlled environment. The apparatus (5) comprises a primary housing (10) defining a primary hollow interior region (11) supported on a main support platform (21) which is mounted on the support pole (3). A secondary housing (14) defining a secondary hollow interior region (15) is coupled to the primary housing (10) by a tubular coupling element (17) which defines a communicating passageway (18) for communicating the primary and secondary hollow interior region (11,15). The secondary housing (14) comprises a lower secondary shell (68) of polycarbonate material and an upper secondary shell (73) which form the secondary hollow interior region (15). A PTZ camera (7) is located in a central first chamber (87) of the secondary hollow interior region (15) and eight first cameras (6) are located in the secondary hollow interior region (15) spaced apart at 45° intervals around the central first chamber (87). Medium and low voltage panels (59,60) are located in the primary hollow interior region (11) for controlling and monitoring data from the cameras (6,7) and the infrared heat detectors (8). An air conditioning unit (31) located in the primary housing (10) controls the temperature of air within the primary and secondary hollow interior regions (11,15) in order to maintain a controlled temperature environment within the primary and secondary hollow interior regions (11,15). An electrically powered circulating fan (130) located in an air accommodating duct (120) which extends from the primary hollow interior region (11) into the secondary hollow interior region (15) through the communicating passageway (18) circulates air from the air conditioning unit (31) between the primary and secondary hollow interior regions (11,15).