I too react to metals and a little to neoprene or Buna-N (nitrile) such as rubber O-rings. I do OK with stainless steel, but 24/7 I'd eventually react to that as well. I got a 100% silicone ring from Mr-S-Leather.com and I don't react to it at all. Another nice thing about the pure silicone product is that it's stretchy enough that you can easily get into a ring that is snug fitting. A really inexpensive ring that won't cause skin reactions or set off metal detectors can be had with industrial Teflon™ O-rings. You can get them in 1/16 inch increments so getting the perfect size is easy. They only cost a buck or two apiece and to get the effect of a wide cock ring I'll put on a stack of three of them. For someone new to wearing cock rings I'd recommend getting a batch of rubber O-rings (which only cost 10 or 20 cents apiece) in different sizes to experiment with the fit and feel. Then if you don't like the rubber rings you'll at least know what your perfect size is before moving on to something more expensive.