A geologist walks out alone. Nobody expects to hear from them until evening. If something happens at ten in the morning — a fall, a snake, a heart, a wrong turn — nobody starts looking until dark, and by then the search area is enormous.
This closes that gap. You say where you are going and when you will be back. If you do not check in, the alarm raises itself — and it hands your contact your route, your last known position, and the time you were last moving.
Someone in trouble often cannot call for help. That is the whole point: this does not need you to be able to act.
A check-in system only works if someone is expecting the check-in. Send them the plan before you leave so they know what to do and when.
Fill in the plan above.
It works with no signal. The countdown, the alarm and the pre-written message all run on the phone. When you next touch signal — even for a moment on a ridge — the message is ready to send with one tap. It is not a satellite beacon and does not replace one for genuinely remote work; it is the thing that makes sure somebody notices, at the right hour, that you have not come back.