Abstract: A method and apparatus for continuously monitoring and telemetering the condition of the vacuum pressure in the intake manifold of an automotive vehicle. The vacuum pressure is continuously sampled by a vacuum-pressure-sensitive device having one end that moves responsive to changes in the vacuum pressure. Mounted on the movable end of the device is a scanning arrangement that moves a pair of metal strips across the front of two light barrier devices as the pressure changes. In the preferred form, the two light barrier devices each consist of a photo-diode transmitter and a photo-transistor receiver. The output from the light barrier devices consists of an electrical signal having three stages as the pressure increases or decreases. The electrical signal passes through a switching arrangement which successively lights up three different-colored lights to inform the operator as to the condition of the vacuum in the intake manifold.