system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How Quartz Crystal Resonators work?
gpt
They rely on a piezo crystal. These crystals have the useful property that they generate a voltage if you squeeze them, and expand or contract if you apply a voltage. They are commonly used in lighters (squeezing them generates a high voltage, which causes a spark), speakers and ultra sound transducers(a rapidly oscillating voltage contracts and expands the crystal) and kitchen scales (putting a weight on them generates a voltage).

As a resonator, the crystal is tuned like a musical instrument to oscillate at a certain frequency, and combined with a small amplifying circuit. If you turn it on, it starts oscillating at a precise frequency, and never stops. Imagine it like a tuning fork, only that it never stops humming as long as you apply a voltage.