The Helites are really, really nice kit. That's the one that Ryan at FortNine recommends (not that he's an expert, but he is a darn entertaining presenter). https://www.youtube.com/watch?v=N2jZryt607U&t=1s

The Helite E-Turtle (non-tethered) unit is currently available in the UK and EU. They are using a recommended fork sensor to help detect crashes quicker. I hear there are some EU vendors that will ship to the US, even though it's technically not available here yet.