An electrically-powered photoelectric device designed for the transcutaneous measurement and display of haemoglobin oxygen saturation (SpO2). The signals are produced by light-emitting diodes (LEDs) and received by a photodetector. The device displays the SpO2 values and may also measure/display pulse rate. It is typically applied to the fingertip or around the wrist, may be single-component (with built-in probe) or multi-component (includes external probe), and may in addition wirelessly transmit measurements to a receiving location (e.g., central station, bedside monitor); it is intended to be operated by laypersons and healthcare providers.