Here's one that you can get from Aerostitch, I'm sure it's available from other vendors.
http://www.aerostich.com/marc-s-visual-alert.htmlI've found it's too easy to miss visual alerts when you've on the gas and really enjoying the road or perhaps distracted by the scenery. I tried all kinds of wired ear plugs, helmet speakers etc. I found being wired up to the bike was a major PIA. I really like an audible alert so I finally broke down and purchased and installed a radar screamer, it works very well, it's also available from Aerostitch.
http://www.aerostich.com/radar-screamer.htmlThis thing is very loud it has 2 volume settings low and high, you can also use the mute button on your detector to quite it down when needed.