A dry adhesive comprising a micro-featured and nano-featured surface, and a compliant surface having a hardness of about 60 Shore A or less, the micro-featured and nano-featured surface and the compliant surface being capable of forming upon contact a dry adhesive bond with each other. The test is used to stop the integration of photocurrent once the accumulated analog voltage has reached a predetermined threshold. The light-emitting components are mounted on the substrate for emitting light in parallel directions that are generally transverse to the substrate. A preferred sensor comprises two pairs of conductivity sensors each having an annular body with a bore corresponding to the diameter of the hose or nozzle bore.