Just wireless power beamed through the air by a router, much like Wi-Fi. The potential benefits for medical devices, sensors, cameras, and a host of other battery-powered gadgets are easy to grasp.
Williams-Guillen and Pheasey found that while poachers tended to sell eggs locally door to door, the InvestEGGator was also able to track long-range transport—one trip was 137 kilometers long, from the beach to central Costa Rica.
That's the premise of the book How to Invent Everything: A Survival Guide for the Stranded Time Traveler, by Ryan North.Without getting into the nitty-gritty details, it gives you the general idea of how things like an electric motor or wifi work. If you can build a radio transmitter, you won't need a clock.