Thumbs up on the ANGI devise from Specialized. Comes attached to some helmets or as a stand alone add on and connects through blue tooth to your phone. I have one, it was on my new helmet. It will send a text message to my wife if it detects a significant impact along with my GPS location. It also has a count down from the time of the impact before it sends the message so I can stop an accidental message from being sent. Just extra insurance for somebody out by themselves. Nothing else required, other than the cell phone you probably already have, not much money. Potential life saver. I like it.