Methods and apparatus relating to a photodiode-augmented infrared (IR) motion sensor are provided. The IR motion sensor can be used to sense mid-IR range radiation emitting from a person. Within the IR motion sensor, incident mid-IR range radiation impinges on an IR sensing element situated behind a Fresnel lens. Thus, when the person crosses a particular region in the range of the IR motion sensor, the IR sensing element detects a change in radiation signature, and can subsequently notify another system, such as a security system, of the change. The IR motion sensor also includes an ambient light-sensing element configured to provide information used to perform a quality check, such as to rule out “false positive” outputs, on information output from the IR sensing element.