the tubular housing 12 an end 50 of the shock tube is exposed to a composition 52 which is used to adhere the magnet within the housing at the rest position optionally the composition 52 is an energetic material so that when exposed to a shock wave which is produced at the end 50 when the shock tube is ignited it is also ignited and thereupon emits energetic material at a relatively high pressure which exerts force on the magnet 40 fig2 shows the tube 30 on an enlarged scale positioned inside the tube are two thin wires or links 60 and 62 respectively which are close to the first and second ends 34 and 36 and which traverse the hollow interior 38 the magnet 40 has a circular cross sectional shape with a diameter which is slightly less than the diameter of the hollow interior 38 a small seal 66 is fixed to a periphery of the magnet and extends circumferentially around the magnet abutting an inner wall 68 of the tube 30 effectively in a gas tight manner the control circuit 24 fig1 includes a communication module for communicating with a programming or testing machine using electromagnetic principles for example of the kind described in.