The invention comprises a reflector with a fastening device for an animal collar. The reflector includes a base plate with an inner surface and an outer surface. A clip, which is substantially U-shaped, runs over the inner surface, the end of the first leg of the clip being fastened by means of a movable connection to a first side of the base plate, and the end of the second leg being suitable for being irreversibly fastened to a side of the base plate opposite from the first side. On the outer surface of the base plate there are triple prisms. On the inner surface of the base plate there is/are one or more spacers. The invention also comprises a collar containing an active substance which can leave the collar over the entire length. At least one of the reflectors according to the invention is fastened to the collar. The invention also comprises a system comprising a collar containing an active substance which can leave the collar over the entire length and at least one of the reflectors according to the invention.
