Here's a fun experiment: Try counting the electronic sensors surrounding you right now. There are cameras and microphones in your computer. GPS sensors and gyroscopes in your smartphone. Accelerometers in your fitness tracker. If you work in a modern office building or live in a newly renovated house, you are constantly in the presence of sensors that measure motion, temperature and humidity.
Sensors have become abundant because they have, for the most part, followed Moore's law: they just keep getting smaller, cheaper and more powerful. A few decades ago the gyroscopes and accelerometers that are now in every smartphone were bulky and expensive, limited to applications such as spacecraft and missile guidance. Meanwhile, as you might have heard, network connectivity has exploded. Thanks to progress in microelectronics design as well as management of energy and the electromagnetic spectrum, a microchip that costs less than a dollar can now link an array of sensors to a low-power wireless communications network.