The sensor had to affix to two hundred thousand cargo refrigerator containers, it had to be able to measure their humidity, temperature, and whether they had suffered any damage, and it had to broadcast that data to their headquarters, and—this was the real catch—the sensor had to operate without batteries and be able to last ten years, because they couldn’t be changing them all the time. In two weeks, AT&T engineers built a prototype of a sensor, half the size of a shoe box, that could affix to every Maersk container and was powered by a combination of solar and kinetic energy.
