A magnetic device for capturing metal wear particles in suspension in a lubrication fluid, the magnetic device being for inserting in a straight-line insertion direction of the magnetic device into a wall of a casing via a through orifice serving to put an inside volume of the casing containing the lubrication fluid into communication with an outside volume outside the casing, the magnetic device presenting a longitudinal axis X, the longitudinal axis X being for putting into coincidence with the direction for inserting the magnetic device into the casing, the magnetic device comprising a permanent magnet suitable for attracting the metal particles and a presence-detector member for detecting the metal particles attracted by the permanent magnet.