Abstract: A sleep detection and alarm system includes a sensor for sensing physiological changes in a user indicating the onset of sleep, an alarm, and an alarm activation mechanism connected to the sensor for sounding the alarm upon detection of the changes by the sensor to awaken the user. The sensor preferably includes a wrist band, an instrument housing mounted to the wrist band and containing a power source, a microprocessor, a piezoelectric crystal for sensing pressure variations between the user wrist and the wrist band, and a mechanism for feeding electronic information in the form of an analog signal to the microprocessor for processing and selectively sounding the alarm. The system preferably additionally includes a filtering mechanism for filtering the analog signals before they reach the microprocessor for removing sudden variations and non-sinusoidal components of repetitive heart and blood stream sounds, so that only continuously varying signals are sensed and analyzed.