PURPOSE: To precisely monitor the operation of a pyrotechnic transmission line by operating a safety device by one ignition of a pair of pyrotechnic transmission lines, and connecting the other end side of a conduit connected to one end of a signal means emitting a light signal to a display means through a sensor means.

CONSTITUTION: A vehicle safety device is provided with a seat belt tensioner 13 and an air bag pump 12 having a pair of ignitable pyrotechnic transmission lines 15, 17; 14, 16 connected thereto, respectively, and each pyrotechnic transmission line 14-17 is connected to a chamber 40 within a metallic ignition manifold 56. The ignition manifold 56 has a pair of minute detonators 50, 52 to ignite the pyrotechnic transmission lines 14, 16 in the chamber 40 by the gas and flame generated from the detonators 50, 52 by ignition, and the detonators 50, 52 are electrically connected to an impact sensor 60 by a pair of wires 53, 55; 55, 57. One end of a conduit 22 for transmitting a signal is connected to a signal generating source 62, and the light signal transmitted through the conduit 22 is received by an optical sensor 66 to operate an indicator 68.