I suppose if you don't stray far from a mobile signal then this might be handy: https://icedot.org/site/crash-sensor/ ... but what if you stop for a slash or for cake and happen to bang your helmet?

For me, the fact it can only transmit via an iphone app means it's a non-starter.

so whacking your helmet on something triggers the sensor and begins a countdown. What stops it? movement presumably?