In a navigation device assisting a driver of a vehicle to drive safely by presenting accurate information at the right time what is going on around hisher vehicle, an obstacle detection part detects any obstacle with the help of external information monitored by an external monitor part. In operation of the system, mixed incoming signals 12 having known interference and unknown emission components can be effectively separated, permitting a virtually instantaneous separation of the known interference from the unknown emissions and permitting an unobscured monitoring andor characterization of the extracted unknown emissions 21, if desired. A low bias RF voltage is provided during the etching process. During engine starting, the circuit enables the visual indicator in response to a condition of the start switch and a low fluid sensor, and disables the audible indicator. The semiconductor chip may be surrounded by the upper and the lower circuit substrates, and molding resins. The system comprises two elements: a positive vapor block in the form of an elastomeric boot or folded diaphragm disposed across the pintle interruption, and a pintle shaft bearing disposable in the valve’s body and sealingly secured to the boot or diaphragm.