Beep-Free buckles are metal free, nickel free and are undetectable by metal detectors. That's because they are made from a special polymer giving them the strength and style of a typical metal buckle, yet setting them uniquely apart at security checkpoints, metal detectors and for people with metal allergies. There is no nickel, or metal of any kind in these buckles. They are completely hypoallergenic. They come in both Standard (30mm) and Standard + (35mm) sizes and your choice of three colors.