Digital Smoke Signals
This is an idea I originally submitted to NPR Sci-Friday for their #MessageChallenge:
In an area deprived of internet access, you can create an ad-hoc network by firing a flare-gun and then bouncing laser light off the smoke. Working much like the first passive satellites put into space, a single puff of smoke provides a shared reflective target for everyone on the ground to use. For the duration that the smoke is in view, any number of people can send and receiving data at Gigabit speeds. The system is essentially a smart phone connected to a handheld laser modem. My mockup DIY laser modem consists of a soup can containing a Raspberry Pi microcomputer, a modulated laser transmitter, and a photodiode monocular telescope for a receiver. There would be a shared smartphone app that would coordinate the signal traffic and negotiate new connections in realtime.