The iPhone was mentioned near the top of this thread, but no one commented or provided details, so I looked it up.
ShotTimer is an iPhone app that doesn't have all the bells and whistles of the dedicated devices mentioned here, but the cost is currently
FREE, so for those of you who already have an iPhone, you can't beat this deal.
I happen to have a set of the new Apple In-earphones and they block a LOT of outside noise. The inline mic can be used to pick up the shots fired and a set of earmuffs would give you plenty of hearing protection without missing the start buzzer through the earphones.
If you're practicing alone this seems to be a perfect solution. Since you can't save multiple results you can just email each set to yourself and study them later. (The emails it produces are pretty nice!)
And remember,
it's free!