A proximity sensor for a mobile telephone device (300,500,600,700), the proximity sensor comprising: a proximity module (302,702) having an emitter to emit light in an emitter field of view 'FOV' and a detector to detect light in a detector FOV, the proximity module configured to generate a signal that is a function of the emitted light and of the light incident on the detector in the detector FOV, wherein the signal is indicative of the presence of a target external to the mobile telephone device; a lens separated from the proximity module by an air gap, the lens having i) a transmissive portion in alignment with the emitter FOV and with the detector FOV, and ii) a non-transmissive portion that extends over an area that is opposite the detector; and an optical routing module (330,530,630,730) secured within the air gap for redirecting the detector FOV and for bringing it into alignment with the emitter FOV, the optical routing module comprising a transmissive-reflective surface (322,522,622,722) in alignment with the emitter FOV, with the detector FOV, and with the transmissive portion of the lens, wherein the transmissive-reflective surface is oriented at an angle of approximately 45° ± 10° with respect to the emitter FOV, and wherein the optical routing module is configured: to guide the emitted light transmitted by the transmissive-reflective surface through the transmissive portion of the lens to the exterior of the mobile telephone device; and to guide target-reflected light collected by the transmissive portion of the lens to the detector by reflecting the target-reflected light using the transmissive-reflective surface, wherein the target-reflected light has been reflected by the target external to the mobile telephone device. a proximity module (302,702) having an emitter to emit light in an emitter field of view 'FOV' and a detector to detect light in a detector FOV, the proximity module configured to generate a signal that is a function of the emitted light and of the light incident on the detector in the detector FOV, wherein the signal is indicative of the presence of a target external to the mobile telephone device; a lens separated from the proximity module by an air gap, the lens having i) a transmissive portion in alignment with the emitter FOV and with the detector FOV, and ii) a non-transmissive portion that extends over an area that is opposite the detector; and an optical routing module (330,530,630,730) secured within the air gap for redirecting the detector FOV and for bringing it into alignment with the emitter FOV, the optical routing module comprising a transmissive-reflective surface (322,522,622,722) in alignment with the emitter FOV, with the detector FOV, and with the transmissive portion of the lens, wherein the transmissive-reflective surface is oriented at an angle of approximately 45° ± 10° with respect to the emitter FOV, and wherein the optical routing module is configured: to guide the emitted light transmitted by the transmissive-reflective surface through the transmissive portion of the lens to the exterior of the mobile telephone device; and to guide target-reflected light collected by the transmissive portion of the lens to the detector by reflecting the target-reflected light using the transmissive-reflective surface, wherein the target-reflected light has been reflected by the target external to the mobile telephone device. to guide the emitted light transmitted by the transmissive-reflective surface through the transmissive portion of the lens to the exterior of the mobile telephone device; and to guide target-reflected light collected by the transmissive portion of the lens to the detector by reflecting the target-reflected light using the transmissive-reflective surface, wherein the target-reflected light has been reflected by the target external to the mobile telephone device.