Device for protecting an article against theft and/or for identifying it, comprising a tag (B) with a passage able to accept a metal pin (F, 8) passing through the item or attached to a lanyard surrounding the item, the tag comprising means (E) for locking the pin in the passage and preventing it from being extracted without a detacher being present, a first face (1a) of the tag which face faces towards the pin being essentially planar, it being possible for the pin to be attached to a head (K), the size of which corresponds to that of the first face of the tag; the tag (B) has a peripheral flank (2) equipped with a translational-guidance means (2) able to collaborate with a cylindrical guide surface provided in a housing (3) of the detacher, and the second face (1) of the tag, remote from the head of the pin, is planar and essentially parallel to the first face.