Hearing Damage Monitor

There are a lot of incredibly loud public environments now, from busy streets to crowded bars with loud music, to all day rock concerts, to airplane tarmacs etc., and there is increasing risk that the current and next generation of kids will have significant hearing problems. I wish I had a device with a microphone and a simple guage to tell me how loud the room i'm in really is. A simple circuit could also keep track of how long I have been exposed to these volumes and advise me when the hearing damage factor is getting too much. (Hearing damage is roughly proportional to the product of the volume and the exposure time for continuous sound). The guage would be simple to read at a glance with green (quiet), yellow (hearing damage unlikely), Orange (hearing damage likely in minutes or hours) and Red, (Hearing damage imminent). I'd love to be able to give these to folks sitting in the front all day at concerts without earplugs so they could have an idea how messed up their ears are going to be in a few years.