Here's a great idea - and a free one at that. Jared Morse has recently launched a web app to help solve issues such as the one Aron Ralston ran into in Utah several years ago.
After registering your trip, ShouldBeBack.com sends out an email and a text message to your emergency contacts if you're late in returning at your predetermined time.
Here's how it works:
You create a trip and provide ShouldBeBack.com with emergency contact information. At the time you indicated that you should be considered late they will send you a text message. If you reply "back" to this text, no further messages will be sent out.
If you don't reply to this first text, they will send a second text to you with the same prompt.
If they still don't hear back from you, a third text is sent, as well as a text and email to your contacts to let them know you're late. This email will contain information about your trip.
If you're in trouble or danger, you can reply "help" when responding to one of the texts and ShouldBeBack.com will immediately text and email all of your contacts to let them know.
One of the fundamental rules of wilderness adventure is to always let someone know where you're going, and when you expect to be back. This app provides an excellent and easy way of giving yourself a lifeline in the event of becoming lost or injured while out on the trail.