Reply to the message (or check in on the website) within 5 minutes and all is well. If you don’t check in, the service alerts a list of emergency contacts that you set up ahead of time. Of course, you can always extend your ETA or check in early.
Kitestring is free and doesn’t even require downloading an app onto your phone. To get started, click here.
They seem to have thought of every contingency, such as can an attacker check in on your behalf, or pressing a duress code if something bad is happening right now. Check out the Kitestring FAQ here.