I posted this in one of the groups I belong to, but I think it's good information so I'll post it here.
Anyway, since I've worn a belt for several years, various models, cb-2000, cb-3000 and currently a my-steel, so I've got some experience. As for the possibility of an accident and being rushed to the emergency room, could it happen, yes. Has it happened to me, no. I think accidents occur rarely and I will take my chances. Also, since I'm in a full steel belt it's not like I could easily cut it in an emergency. Yes, I'm sure a pair of bolt cutters would make short work of it if I really needed to get out but for obvious reasons I don't carry those around with me on a daily basis.
Also, I do find that I am more cautious to avoid an accident now while locked. I find that I drive more defensively and generally don't speed. I used to be the person that if I was on a two lane road behind someone going exactly the speed limit, I would take the first opportunity to floor it and pass them. Now, I just kinda sit back at a safe distance knowing that I'll get to my destination eventually. I guess this also saves gas and wear and tear on the car, so that's a good thing.
As for being involved in an accident while wearing the belt, yes, I have. It was a minor skiing accident where I twisted/sprained my knee. Ski patrol brought me down in the sled and I was wearing a cb at the time, either the cb2k or the 3k, don't quite remember, doesn't really make a difference. For this, my cb was not discovered at all. At the mountain clinic, I pulled my pant leg up, they looked at my knee, and said that I should go to a real doctor to have it looked at. Yes, they offered to transport me via ambulance to the local hospital, but I declined, I told them I would go to my regular doctor at home. They bandaged my knee up and gave me an ice pack, set of crutches and I believe a hot chocolate as well. I did ask them if they would be nice enough to get my car from the parking lot a ways away and they did. I drove home (not an easy task driving a stick shift with one leg), followed their instructions and went to my local clinic after I unlocked. At no point in time would I have had to take my pants off at either of these places so it was not a big deal.
As for being discovered, I don't think I ever was, but I had one close call. This was when I was living in a college apartment with a few friends of mine. It wasn't any of the friends that saw, but what happened was our bathroom didn't have a doorknob lock, just a hook & eye latch. All of our housemates knew this and were quite respectful, if the door was closed, that meant it was occupied. Well, one day the landlord sent a plumber over to fix something in the bathroom, the shower I think. I didn't realize that the plumber was here and had gone down to the basement to shut the water off, so I was sitting on the toilet, door closed, with the latch and the plumber doesn't knock, and just tries to come in. The door only opened about an inch or two until he realized I was inside. I know he saw I was on the toilet, and there's a chance that he could have caught a glimpse of the cb, but I don't think he did. At least he never said anything if he did and I never saw that plumber again after that. That's all I got, and that's from about 7 years of wearing chastity belts.