Check if display is at sleep or receive sleep notifications

Question

I have an application utility which becomes useless when there\'s no user. So, in order to save resources, I\'d like it to know when/whether display is at sleep.

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Answer 1

This is response to a question asked a while ago - but I thought it would be useful to add my answer.

NSWorkspace has a couple of notifications for when displays wake and sleep: NSWorkspaceScreensDidSleepNotification and NSWorkspaceScreensDidWakeNotification