Supposedly the Apple Watch 4 actually has a feature that will alert your emergency contacts if it detects you’ve had a hard fall. https://support.apple.com/en-us/HT208944
It will give you the opportunity to turn that alert off by buzzing your watch and giving you the chance to choose to stop the alert if you are ok, but if not, it will notify your emergency contact.
There are a couple of bike helmets that have built in fall detection devices – I have contacted Specialized to see if their unit would work on a riding helmet, and they say it would. But, I’m not enthusiastic about the attachment mechanism.
I would love for a helmet to be developed that had bluetooth capability, and fall detection like a couple of the bike helmets. I think for endurance riders or anyone that trail rides near a road, the ones that also have lights front and rear would be helpful. I would love to know if anyone from R&D in our helmet companies were developing such a thing!