I closed my 2020 M1 MacBook Pro (running Big Sur) at 9:57 p.m. I have my MacBook Pro set to passcode lock after 5 minutes of sleep. I opened my Mac at 10:09 p.m and my MacBook was not asleep/unlocked because it opened up to the Safari page I was on. This has happened before once as well (Mac should have been on Lock Screen/asleep but was not).

It had been well over 5 minutes, so shouldn't my MacBook have gone to sleep and went to the lock screen when I opened it back up? Do you think that my MacBook probably never went to sleep, and thus didn't passcode lock? If so, what kind of things could have caused that.

I checked terminal and "PreventUserIdleSystemSleep" had a "1" but said that it was due to the display being on. Are there other things that could sometimes prevent my MacBook from going to sleep, and thus not locking?

1 Answer 1


Launch Activity Monitor from Applications/Utilities

From the View menu select All Processes then in the main window click the CPU tab.
Right click anywhere in the header & add the last item in the list - Preventing Sleep [you may need to enlarge the window to see it.]

Click the Preventing Sleep header once to sort 'yes' to the top.
Some of the processes there will automatically stop preventing sleep when they need to [which makes it a bit tougher to judge] but you might find an obvious one, maybe a browser tab playing a radio station or similar.

In this screenshot, the web page would be prime suspect [time machine is currently running to schedule, & screensharing is because I'm remoted into that computer]

enter image description here

  • Ah there were some things, but nothing weird (probably cause it stopped). So are you saying that there could be processes that may prevent the Mac from sleeping even when the lid is closed, and thus prevent it from going to the Lock Screen? Just getting paranoid that someone might be hacking into my Mac while it's asleep or something. Aug 8, 2021 at 17:54

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .