I just received an email from Specialized.
There seems to be a new helmet mounted crash sensor.
It is placed on your helmet and in the event of a crash, it automatically calls your pre-designated contacts unless you abort in a certain period of time.
Since it uses your mobile phone, no subscription is required.
As full face helmet this is the only model
www.specialized.com/gr/en/s-works-dissident-with-angi/p/162033
Euro 419
any reason I could not just mount this on my TSG?
https://www.specialized.com/gb/en/angi-crash-sensor/p/170203
No reason. This is why I wrote helmet mounted crash sensor and not helmets with crash sensor.
Specialized makes bike helmets which are not always suitable for our application but since they sell the sensor as a stand alone for $50, I think it is a good deal.
was just about to order one, reviews make me worry a little - still think its might be worth the risk (if mounted right)
Most negative reviews seem to be about the fact that you either need a Specialized helmet or double sided tape to attach it.
I believe most people in this forum have the DIY skills to make a 3d printed bracket or come with some sort of solution.
I actually tried this at work several month ago. You do need a subscription or some kind of payment other than $50 msrp. The sensor will send signal to your phone then your phone will send a email with your gps location if it senses a sudden rotation.
This is from their email
Anyway it’s long time ago I do remember ask my boss for company credit card for a in app payment. Maybe they changed. 
I wish there was an open source version that could be added to existing Esk8 apps.