Power is a limit. When creating an electrical device, it needs some way to draw energy, or else it might as well be an awkward, inert rock. The easiest way is to tap into the grid, limiting the device's mobility to the length of a power cord, or using batteries, which have a limited lifetime. For most everything, one or the other is a workable solution, but if an architect wanted to embed sensors in a tunnel or a bridge to measure stress over a lifespan of decades, they'd need a complicated system for wiring in those sensors or replacing their batteries. But there may be another option. The Wireless Identification and Sensing Platform (WISP) is a programmable wireless computer that draws power from radio waves.