A photoelectric device designed to be applied externally to a body site (e.g., fingertip, ear lobe, bridge of nose, toe, or bridge of the foot) for the transcutaneous measurement of haemoglobin oxygen saturation (SpO2) in arterial blood using signals produced by a light-emitting diode (LED) and received by a photodetector. The signals are subsequently transmitted to an oximeter/monitor (not included) which measures and displays the SpO2. The is a single-use device.