Abstract: A highly sensitive electronic blood pulse sensor and readout device is disclosed which is self-powered and can be mounted on the subject's wrist. The sensor portion has a plurality of light emitters which are arranged to emit pulsed infra-red light waves having a wavelength readily absorbed by blood constituents, and a plurality of light detectors highly responsive to the emitted wavelength. The level of detected illumination is used to control by feedback the level of emitted illumination, in order to compensate for variations in flesh translucency. A separate "noise" responsive sensor is used to counteract the noise-inducing tendencies of motion.