All your piezo are belong to us

Microphones are everywhere: smartphones, IoT devices, and so forth. Speakers can be used as microphones too. But what is even more ubiquitous than either of those? Piezo buzzers. They are literally everywhere: smoke detectors, thermostats, electric kettles, fridges, washing machines, computers, and the list goes on. This post is about finding out whether piezos can be used as microphones.