A hazard detector (104, 400) comprising: a front casing that is coupleable with a back plate to define a housing having an interior region within which one or more components of the hazard detector (104, 400) are contained; a passive infrared sensor device disposed within the interior region and positioned to face a room (152, 1412) within which the hazard detector (104, 400) is positioned, the passive infrared sensor device having a field of view into the room (152, 1412) such that objects or individuals present in the room (152, 1412) and within the field of view are detectable by the passive infrared sensor device, the passive infrared sensor device being communicatively coupled with a circuit board of the hazard detector (104, 400) so as to provide information thereto and/or receive information therefrom; a button cap component coupled with a button portion of the front casing such that the button cap component is pressable by a user to effect axial movement of the button portion of the front casing to cause the button portion to contact a switch positioned therebehind so that input is provided to the hazard detector (104, 400) by the user, the button cap component having a first side facing the room (152, 1412) and a second side opposite the first side; characterized in that the hazard detector further comprises a cover plate coupled with the front casing, the cover plate being configured to face an occupant of a room (152, 1412) in which the hazard detector (104, 400) is positioned, wherein the cover plate includes a centrally located aperture within which the button cap component is positioned, and in that the button cap component comprises a Fresnel lensing component formed integrally therewith, wherein the Fresnel lensing component is positioned axially in front of the passive infrared sensor device to direct infrared radiation onto the passive infrared sensor device, the Fresnel lensing component being formed on said second side of the button cap component so as to be hidden from external view, wherein the button cap component is transparent to the passive infrared sensor device so that the passive infrared sensor device is able to view objects or individuals through the button cap component. a front casing that is coupleable with a back plate to define a housing having an interior region within which one or more components of the hazard detector (104, 400) are contained; a passive infrared sensor device disposed within the interior region and positioned to face a room (152, 1412) within which the hazard detector (104, 400) is positioned, the passive infrared sensor device having a field of view into the room (152, 1412) such that objects or individuals present in the room (152, 1412) and within the field of view are detectable by the passive infrared sensor device, the passive infrared sensor device being communicatively coupled with a circuit board of the hazard detector (104, 400) so as to provide information thereto and/or receive information therefrom; a button cap component coupled with a button portion of the front casing such that the button cap component is pressable by a user to effect axial movement of the button portion of the front casing to cause the button portion to contact a switch positioned therebehind so that input is provided to the hazard detector (104, 400) by the user, the button cap component having a first side facing the room (152, 1412) and a second side opposite the first side; characterized in that the hazard detector further comprises a cover plate coupled with the front casing, the cover plate being configured to face an occupant of a room (152, 1412) in which the hazard detector (104, 400) is positioned, wherein the cover plate includes a centrally located aperture within which the button cap component is positioned, and in that the button cap component comprises a Fresnel lensing component formed integrally therewith, wherein the Fresnel lensing component is positioned axially in front of the passive infrared sensor device to direct infrared radiation onto the passive infrared sensor device, the Fresnel lensing component being formed on said second side of the button cap component so as to be hidden from external view, wherein the button cap component is transparent to the passive infrared sensor device so that the passive infrared sensor device is able to view objects or individuals through the button cap component.