The present invention relates to an electropyrotechnic initiator comprising: an ignition support (10); an electrical initiation system (11) connecting the ignition support (10) to a source of electricity; and a cap (2) containing at least one explosive composition, the cap being of generally cylindrical shape presenting an open first end (20) connected to the ignition support (10), an opposite second end that is closed by an end wall (21), and a peripheral side wall (22) which presents at least one zone of weakness (3). This initiator is essentially remarkable in that at least one of the zones of weakness extends along a non-closed trace and over a portion only of the side wall (22), i.e. without reaching its opposite ends.