Why does my mouse double-click on a single press?

The switch under the button has worn out. Its contacts have oxidised or the leaf spring has fatigued, so one press produces a bouncing electrical signal that the firmware reads as two clicks. It is a hardware fault, and replacing the switch fixes it permanently.

Why it happens

Inside each main button is a sealed micro-switch: a curved steel leaf spring that snaps against gold-plated contacts. The snap is what you feel and hear. Firmware applies a debounce window, ignoring further transitions for a few milliseconds after the first, so normal contact bounce never reaches the operating system.

As the leaf spring fatigues, the snap gets slower and less decisive, and the bounce lasts longer than the debounce window. The oxide film that builds up on ageing contacts makes it worse by adding intermittent resistance. Past that threshold the operating system genuinely receives two clean click events.

Software fixes that raise the debounce delay do work, but they add input latency and only push the threshold back — the switch continues to degrade.

What to do about it

1. 1Rule out software first: try the mouse on another computer. If it double-clicks there too, it is the switch.
2. 2Switches are through-hole soldered, so replacement is genuinely achievable with a soldering iron and a desoldering pump. Common part sizes are inexpensive and widely sold.
3. 3If you would rather not solder, note the failure mode when buying next — some mice use socketed switches specifically so they can be swapped by hand.