Device for signalling the tripping of an electrical protection unit such as a circuit breaker housed in an insulating housing enclosing a pair of fixed and movable contacts, said movable contact being able to be actuated either manually by a handle linked mechanically to a movable contact support device, said handle being mounted to pivot between a position of closure and a position of opening of the contacts, or automatically via a trip mechanism comprising a magnetic trip with a mobile core that can be activated upon the occurrence of a short-circuit fault and a thermal trip that can be activated upon the occurrence of an overload fault, said movable contact support being mounted to rotate between a position of opening of the contacts and a position of closure of the contacts and linked to the handle by a transmission means so as to form, between the support and the handle, a breakable mechanical link, the activation of one of the trips leading to the breaking of the mechanical link resulting in the separation of the contacts, and so-called first signalling means that can be triggered only upon a short-circuit fault, the so-called first signalling means comprising means for blocking the abovementioned handle in an intermediate position situated between the two positions of the handle corresponding respectively to an open position and a closed position of the unit, upon the occurrence of a fault of magnetic origin, these means being controlled by the mobile core of the magnetic trip, these means comprising a so-called first lever, called return lever, mounted articulated about an axis that is fixed relative to the housing of the device, this return lever comprising a first end part intended to cooperate with the mobile core and a second end part intended to cooperate with the base of the handle, the abovementioned return lever cooperating with the mobile core via a so-called second lever mounted articulated relative to the housing of the unit, said second lever comprising a first end part mounted to rotate about an axis secured to the mobile core and a second end part comprising an attachment element that can cooperate with an attachment element of complementary form belonging to the above-mentioned first end part of the return lever, so that the position of attachment of the two levers (27, 28) relative to one another corresponds to a closed position of the contacts (4, 5) in a normal operation of the unit, and that, upon the occurrence of a fault of magnetic origin, the displacement of the mobile core leads to the disengagement of the two attachment elements (33, 34) relative to one another, this disengagement allowing the return lever to return into a position of blocking of the handle in the abovementioned intermediate position, characterized in that the abovementioned return lever comprises a so-called third end part that can cooperate with an indicator so as to signal the presence or not of a fault of magnetic origin, and in that this indicator comprises a reset means that can be operated by a user so as to return the return lever into a position of attachment with the so-called second lever, after the blocking of the handle in an intermediate position, and do so in order to release the handle and allow its displacement to the open position to continue.