A tamper-resistant by-pass valve prevents an unauthorized user from tampering with the valve when it is in the closed position to block gas flow to a meter being replaced or repaired. The head designed for fixing of a rigid closure is provided with a circular cylindrical wall extending towards the inside of the tube and enclosing an orifice concentric to said inscribed circle and having a large diameter, typically more than 0. To provide an organometallic complex formed by ortho-metalation of an m-alkoxyphenyl pyrazine derivative represented by General Formula below with respect to an ion of a metal belonging to Group 9 or Group 10. Where the photosensitive detector is in a housing with a window through which the light beam enters the housing, the housing can be tilted.