Abstract: The signal transmitter (1) includes a casing (10) which, when installed, is positioned opposite a brake member (8) at decreasing spacing as the wear of the brake lining (6) progresses. The casing (10) contains electrical contacts (31,35,37,39) and leads (41,43,45) the switching states of which are adapted to be changed at a certain wear or heating of the brake lining (6). A plug (51) is guided in the casing (10) for displacement out of an inoperative position in parallel with the direction of wear of the brake lining (6). Upon progressed wear of the brake lining (6) the brake member (8) mentioned presses the plug (51) further into the casing (10). In a terminal position of the plug (51) at least one of the contacts (37,39) is held in a switching position which differs from the inoperative position, whereby an alarm signal is released.