Abstract: The disclosure relates to an air pressure sensor comprising a first air passage, a branch passage having an opening into the air passage, a sensor in the branch passage responsive to variation in air pressure in the opening and jet means for air flow through the first passage adjacent the opening to the branch passage to create an increased depression in static pressure as compared with the remainder of the air passage to enhance the response of the pressure sensor in the branch passage when air flow through the first passage occurs. The air passage terminates in a probe having an orifice to be opened and closed by the absence of and presence of a surface in contact with the probe so that the pressure sensor indicates whether or not the probe is in contact with the surface.