A security device for attaching around a generally annular article to be protected from theft, said device comprising: a rigid housing defining an interior chamber with an entry port; wherein the housing has a concave inner perimeter and an outer perimeter; a ratchet strap which is connected to and extends outwardly from the housing and has a series of one-way locking teeth formed thereon; a locking mechanism disposed in the interior chamber for lockably engaging one of the locking teeth when the strap is inserted through the entry port to secure the strap in a locked position in which the strap and inner perimeter of the housing define therebetween an article-receiving space adapted to receive the generally annular article; wherein the strap and inner perimeter of the housing together assume a generally circular configuration which is substantially concentric about a vertical axis which in use passes centrally through the generally annular article; and wherein the housing has first and second circumferentially opposed ends; characterized in that the housing has a first outer surface which tapers radially outwardly and downwardly relative to the vertical axis from adjacent the inner perimeter to adjacent the outer perimeter and a second opposed outer surface which tapers radially outwardly and upwardly relative to the vertical axis from adjacent the inner perimeter to adjacent the outer perimeter so that the first and second opposed outer surfaces (40, 42) taper radially outwardly and toward one another from adjacent the inner perimeter to adjacent the outer perimeter; each of the tapered outer surfaces (40, 42) extends circumferentially from adjacent the first end to adjacent the second end and defines a respective substantially linear intersection with a vertical plane in which the vertical axis lies; each linear intersection is disposed centrally between the opposed ends (32, 34) and extends from adjacent the inner perimeter to adjacent the outer perimeter; and each linear intersection and a plane perpendicular to the vertical axis defines therebetween an angle (Y, Z) within a range of 25 to 60 degrees. a rigid housing defining an interior chamber with an entry port; wherein the housing has a concave inner perimeter and an outer perimeter; a ratchet strap which is connected to and extends outwardly from the housing and has a series of one-way locking teeth formed thereon; a locking mechanism disposed in the interior chamber for lockably engaging one of the locking teeth when the strap is inserted through the entry port to secure the strap in a locked position in which the strap and inner perimeter of the housing define therebetween an article-receiving space adapted to receive the generally annular article; wherein the strap and inner perimeter of the housing together assume a generally circular configuration which is substantially concentric about a vertical axis which in use passes centrally through the generally annular article; and wherein the housing has first and second circumferentially opposed ends; characterized in that the housing has a first outer surface which tapers radially outwardly and downwardly relative to the vertical axis from adjacent the inner perimeter to adjacent the outer perimeter and a second opposed outer surface which tapers radially outwardly and upwardly relative to the vertical axis from adjacent the inner perimeter to adjacent the outer perimeter so that the first and second opposed outer surfaces (40, 42) taper radially outwardly and toward one another from adjacent the inner perimeter to adjacent the outer perimeter; each of the tapered outer surfaces (40, 42) extends circumferentially from adjacent the first end to adjacent the second end and defines a respective substantially linear intersection with a vertical plane in which the vertical axis lies; each linear intersection is disposed centrally between the opposed ends (32, 34) and extends from adjacent the inner perimeter to adjacent the outer perimeter; and each linear intersection and a plane perpendicular to the vertical axis defines therebetween an angle (Y, Z) within a range of 25 to 60 degrees.