This is a simple obvious addon that every connected portable device could implement. When I bought my fist and last smartphone (Android 2 at that time) after noticing it had an accelerometer on board I immediately thought of an app that could detect a fall when going at some speed, then start beeping for like say 10 seconds and in case the user didn't stop it (as in signaling "I'm ok") it would call emergency numbers sending them coordinates through SMS. I had other things to do at that time, and it seemed so obvious that I thought it already existed or someone soon would create something similar.
This really wouldn't work for phones. The accelerometer needs to be very high precision, which is why it only works on very recent Apple Watch models. The accelerometer also needs to be running all the time, even while the main processor on the device is sleeping. Also you need a reliable way to detect that the device is firmly attached to a human; it's not acceptable to call 911 when a phone falls on its own.
