A chassis having a cover moveable between open and closed positions and circuitry for detecting whether the cover is in the open or the closed position. The circuitry includes a transmitter of optical energy disposed at a fixed position within the chassis for transmitting pulses of optical energy at a predetermined frequency and a receiver for optical energy disposed at a fixed position within the chassis. A reflector is mounted to an inner surface of the cover and is disposed in a path to intercept and then reflect the intercepted transmitted energy to the receiver when the cover is moved to the closed position and being disposed away from the path to prevent the transmitted energy to be intercepted and then reflected to the receiver when the cover is moved to the open position. The detection circuitry indicates whether the cover is in either the open or the closed position selectively in accordance with whether the transmitted energy is reflected to the receiver is above or below a predetermined threshold level and whether at said predetermined frequency.