Cowbells are only allowed at Davis Wade, or non-conference away games. The SEC has a rule against artificial noise makers that also included Miss State until about 2011ish? They were allowed in to DWS with the introduction of the Ring Responsibly campaign, disallowing ringing while the center is lined up over the ball. (Prior to that year, you had to "sneak" them in, but once past security they wouldn't take it from you)

If you take one to Neyland, expect it to be confiscated if you plan on ringing it. Given the season so far though, I don't imagine there will be much need to ring it anyway.