Abstract: A housing is shaped and sized to conform to the user's ear in the manner of a hearing aid. Within the housing is a position-responsive switch and a second generator responsive to the switch. An arm extends from the switch exteriorly of the housing to allow easy adjustment of the switch's position relative to the housing. In use, the housing is positioned behind the user's ear and the switch adjusted so that the sound generator is off. Should the user's head nod, the sound generator will be actuated, alerting the user by both bone conducted and atmospherically conducted sound, to prevent his falling asleep.

Abstract: This invention is directed to improved pseudorandom noise velocimeters and methods therefor, using the Doppler effect, to enable the external measurement of the speed of a moving target within a fixed conveying medium. In accordance with a preferred embodiment of the present invention a continuous pseudorandom ultrasonic noise signal formed by a repetitive code C having n different elementary segments S is radiated. Correlation between a received echo and the delayed radiated signal is accomplished by proceeding successively for each elementary segment, using a different measuring band, for a period corresponding to the period of each segment. The correlation values thus obtained are then stored and thereafter a Doppler low frequency curve is reconstituted by regrouping the correlation values corresponding to the different elementary segments of the repetitive code.