Apple Watch 9 randomly unlocks Mac mini

I experience this too with my Mac mini.

After some experimentation, I've found that the issue is my mouse. Sometimes the mouse laser will flick just a tiny bit for whatever reason, and that'll wake the Mac and then unlock it with my Watch. To test this out simply unplug or turn off your mouse and watch the behavior go away.

Apple could probably fix this by making mouse movements required to wake a Mac slightly larger.

OceanMew wrote:

I experience this too with my Mac mini.

After some experimentation, I've found that the issue is my mouse. Sometimes the mouse laser will flick just a tiny bit for whatever reason, and that'll wake the Mac and then unlock it with my Watch. To test this out simply unplug or turn off your mouse and watch the behavior go away.

Apple could probably fix this by making mouse movements required to wake a Mac slightly larger.

Might want to look into that, as — on most any recent macOS version — pressing a keyboard key, opening the laptop lid, or clicking a mouse button can be set to wake the Mac, but mouse movement alone should not wake it:

https://support.apple.com/guide/mac-help/put-your-mac-to-sleep-or-wake-it-mh10330/mac

Is yours an Apple Magic Mouse, or...?

It has been my experience moving a third party wired mouse will absolutely wake a sleeping Mac. I might try a wireless one when I get around to looking for where I put it.

My experience is that a sleeping Mac will not wakeup from mouse movement.

However, if the Mac is awake, but the screen saver running, or even the screen turned off, the running Mac will respond to the mouse movement, turn on the screen, and allow the Apple Watch to unlock the Mac.

Many many years ago, like with Mac OS Classic (version 9 and older), a wired mouse could wake up a sleeping Mac.