A covered chamberless particulate detector comprising: a chamberless detector configured to produce a signal when particulate sensing events occurs; one or more optical emitters disposed on the chamberless detector, configured to emit one or more emitting cones of light; one or more optical sensors disposed on the chamberless detector, defining one or more receiving cones; and a protective cover (30; 130; 230; 330; 430; 530; 630; 730) defining an inside region and an outside region, the protective cover (30; 130; 230; 330; 430; 530; 630; 730) disposed on the chamberless detector; characterised in that: the protective cover (30; 130; 230; 330; 430; 530; 630; 730) comprises a dome-like structure defining a concave side that is proximate the inside region and a convex side that is proximate the outside region, wherein the protective cover (30; 130; 230; 330; 430; 530; 630; 730) has a plurality of apertures (136; 236; 336; 436; 536; 636; 736) therethrough, the apertures configured to: permit light from each of the one or more emitting cones of light to illuminate the outside region; permit light from the outside region to enter the inside region; and permit fluid communication between the outside region and the inside region; each of the one or more optical sensors is configured to detect occurrence of the particulate sensing events; and each of the one or more emitting cones of light is configured to overlap with each of the one or more receiving cones, thereby creating two or more sensing volumes,_at least one of the two or more sensing volumes is located in the inside region; and at least one of the two or more sensing volumes is located in the outside. a chamberless detector configured to produce a signal when particulate sensing events occurs; one or more optical emitters disposed on the chamberless detector, configured to emit one or more emitting cones of light; one or more optical sensors disposed on the chamberless detector, defining one or more receiving cones; and a protective cover (30; 130; 230; 330; 430; 530; 630; 730) defining an inside region and an outside region, the protective cover (30; 130; 230; 330; 430; 530; 630; 730) disposed on the chamberless detector; characterised in that: the protective cover (30; 130; 230; 330; 430; 530; 630; 730) comprises a dome-like structure defining a concave side that is proximate the inside region and a convex side that is proximate the outside region, wherein the protective cover (30; 130; 230; 330; 430; 530; 630; 730) has a plurality of apertures (136; 236; 336; 436; 536; 636; 736) therethrough, the apertures configured to: permit light from each of the one or more emitting cones of light to illuminate the outside region; permit light from the outside region to enter the inside region; and permit fluid communication between the outside region and the inside region; each of the one or more optical sensors is configured to detect occurrence of the particulate sensing events; and each of the one or more emitting cones of light is configured to overlap with each of the one or more receiving cones, thereby creating two or more sensing volumes,_at least one of the two or more sensing volumes is located in the inside region; and at least one of the two or more sensing volumes is located in the outside. the protective cover (30; 130; 230; 330; 430; 530; 630; 730) comprises a dome-like structure defining a concave side that is proximate the inside region and a convex side that is proximate the outside region, wherein the protective cover (30; 130; 230; 330; 430; 530; 630; 730) has a plurality of apertures (136; 236; 336; 436; 536; 636; 736) therethrough, the apertures configured to: permit light from each of the one or more emitting cones of light to illuminate the outside region; permit light from the outside region to enter the inside region; and permit fluid communication between the outside region and the inside region; each of the one or more optical sensors is configured to detect occurrence of the particulate sensing events; and each of the one or more emitting cones of light is configured to overlap with each of the one or more receiving cones, thereby creating two or more sensing volumes,_at least one of the two or more sensing volumes is located in the inside region; and at least one of the two or more sensing volumes is located in the outside.