A key can move a few millimeters, but the keyboard only needs to detect one event: actuation. Two big approaches:
Inside are two metal leaves. As you press, the stem pushes one leaf until the two touch, closing a circuit. This is simple and widely used.
The switch movement changes a sensor reading without metal contacts touching.
Hall effect: a magnet on the stem changes a magnetic field measured by a sensor.
Optical: the stem blocks/unblocks light to a sensor.
Pros: no contact wear; can enable features like adjustable actuation (especially Hall effect).
Cons: usually needs special PCBs; feel still depends on mechanics, not the sensor.
In many switches, actuation and reset are not identical points. That gap is called hysteresis. It matters for rapid repeats and gaming because it changes how quickly a key can re-trigger.
A switch has noticeable hysteresis: the reset point is higher than the actuation point. What practical effect does this most directly have during fast tapping?
Most people first assume hysteresis is a “feel” change, but it’s mainly about when the signal changes state. If reset is higher, you must let the key rise further before it can actuate again, which can help prevent unintended re-triggers (but can also slow rapid repeats). Spring constant changes and housing expansion aren’t what hysteresis refers to, and it doesn’t inherently change sound or prevent bottoming out.