The Guardall W73820 proximity fobs are designed to replace Guardall Cards W73837 and can be used as a direct replacement. These fobs use 125kHz proximity technology and are sold in packs of 2. Each fob measures 4 x 25 mm.Replacement for Guardall Cards W73837Uses 125kHz proximity technologySold in packs of 2, each fob measures 4 x 25 mm.