A smoke detector with a surface mounted emitter configured to emit light substantially vertically and a surface mounted receiver configured to receive light at an angular distance less than 90° reflected by ambient materials, and a method of operating the smoke detector are provided. The angular distance at which the light is reflected by the ambient materials generates a back scatter effect. The smoke detector includes a housing defining a chamber for receiving the ambient materials, a supporting structure (e.g., a printed circuit board (PCB)) disposed adjacent to the housing, an emitter mounted substantially vertically to an upper surface of the supporting structure, and a receiver mounted substantially vertically to the upper surface of the supporting structure. The smoke detector may also include a controller configured to receive output signals from the receiver (to determine whether a current condition of the chamber indicates a need to trigger an alarm).