However exciting back-country exploring can be, being off the grid and out of touch can present a dangerous situation in emergencies.  The Sonnet Off-Grid Communication Device ($89 for the pair) can put your fears to rest by keeping you connected to other users for as far as nine miles line-of-sight communication without a wireless or satellite connection.

By turning your phone into a virtual walkie-talkie, the Sonnet can do more than keep you in touch in the wilderness, while traveling abroad, dealing with natural disasters, or when you find yourself at crowded events.  The device can create its own network to send instant messages, voice recordings, pictures, and even GPS coordinates with no cellular service or Internet access.  Even better, the Sonnet is dust tight & water resistant, provides end-to-end encrypted communication, and packs a 4000 mAh lithium battery and USB port, so you can charge your smartphone with it.