The invention relates to an electromagnetic trigger, of the differential relay type, comprising: a U-shaped armature (1), the ends of the two legs (4, 5) of which form two coplanar polar surfaces; a pivoting plate (2) that pivots between two positions, in which it, respectively, is at distance, i.e. there is a gap between it and said armature (1) and, in the armed position of the trigger, it makes contact with said polar surfaces and thus closes the magnetic circuit formed by said armature (1) and said plate (2), the hinge (3) of the plate (2) being located in the immediate vicinity of the end of one of the legs (4) of the armature (1); a permanent magnet (6) for biasing the magnetic circuit, placed between the legs (4, 5) of the armature (1) and creating a permanent magnetic force attracting the plate (2) toward the polar surfaces, which magnetic force acts against a return force exerted by a spring (13); and an inductive coil (16) encircling the magnetic circuit, connected, for example, to a circuit to be controlled, with a view to modifying the initial balance between the magnetic force and the return force of the spring (13). The magnet (6) is positioned in the vicinity of the leg (5) of the armature (1) opposite the leg (4) proximate the hinge (3) of the plate (2).