portion 35 is pushed in and for the duration of the pushed in condition the switch 34 may in other words be of the pushbutton type a latching member 36 is located between the electromagnet 32 and the pin 19 and has an arm 37 which is associated with the electromagnet 32 and in fact forms the armature thereof and an arm 38 the member 36 is pivotable about a pivot pin 39 which is mounted in the walls 14 and 15 the arm 37 can abut the pole surface of the electromagnet 37 if desired a non magnetizable intermediate layer may be provided between the pole surface and the arm 37 so that no direct contact between them will take place the arm 38 is formed with a bore 40 in which a retaining member 42 is displaceable by a distance determined by the length of a slot 43 through which the pin 39 extends a prestressed spring 41 bears upon the retaining member 42 which latter has a nose 44 corresponding in shape to the profiling of the detent portions or teeth 22 a spring 45 is mounted on the housing wall 16 and is prestressed in the sense urging the.