Smart phone app or device for when you go down and cannot call for help?

I have been looking for a devise that can sms an emergency number if you are involved in an accident and are unable to call for help. It obviously needs to use the devise's accelerometer/enertial component to detect a sudden unusual event like sudden deceleration and or angle of the bike. When I do a google search, BMW's system comes up but there must be something that does not cost an arm and a leg. I have found a system called Crashdetech, anybody use something similar?