Often, it's hard to recall exactly how you landed and rolled etc. in an accident because it happens so fast. So, if you've had a fall, just replace the helmet. You may think it never hit the ground but it's not worth the risk it entails.
I forget the company but one of them was going to do something like the gridiron football helmets. They were going to have a g-force indicator in them to indicate damage and concussion potential. I'm not sure what became of it.
The shock indicators can possibly help determine if a hit was hard enough to suspect a concussion, but diagnosis of a concussion is based on symptoms.