Here's the deal:
$4.99 at your local grocery store, as thin as a credit card and must be applied to your windshield.
I'm not too comfortable leaving a, what could be, removable sticker on my bike windshield because anyone can take it. The instructions say that it will only work when applied to the windshield... Does TSB think it would work if applied to top of helmet? It's one of those reverse-adhesives, so a piece of tape will have to hold it on...ghetto, but effective.