How it works
A thermistor is a special type of resistor whose electrical resistance changes significantly with temperature. They come in two primary types: NTC (Negative Temperature Coefficient), where resistance drops as it gets hotter, and PTC (Positive Temperature Coefficient), where resistance rises as it gets hotter.
NTC thermistors are incredibly common as cheap, robust temperature sensors in 3D printers, digital thermostats, and battery charging circuits. They are highly non-linear, so converting their resistance into a precise Celsius temperature reading requires solving a complex logarithmic equation (the Steinhart-Hart equation) in software.