the configuration of the tube corresponds to the shape of the downwardly bent channel 11 according to fig2 the bent tube 25 is firmly clamped between circuit support plates 27 by means of screws 28 with blocks 26 adapted to the shape of the tube being interposed therebetween as shown in fig4 the circuit support plates 27 support the switching circuits of the safety turn off means and are provided with openings 29 disposed opposite each other within the range of one of the ends of the bent tube 25 a light emitting diode 30 is fastened in one of the openings 29 and a phototransistor or photocell 31 is fastened in the other in this manner whenever accelerations occur which act upon the acceleration sensor according to fig4 in the direction of arrow 13 the ball 12 oscillates in the bent tube 25 and temporarily interrupts the radiant path between the light emitting diode 30 and the phototransistor 31 contact lugs 32 and 33 respectively of the circuit support plates 27 serve for supplying electrical power to diode 30 and for deriving the detector signals from phototransistor 31 by using the acceleration sensor 4 a safety turn off means for the pressing iron according to fig5 can be constructed in a manner such that the.