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What is Snow Leopard's behaviour when there is a power failure and it is connected to a UPS, and it is in sleep mode? Will the UPS alarm notification wake OSX?

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up vote 1 down vote accepted

Any change on the USB bus should trigger a wake from sleep, so that the system can see what has happened... (For example, place your system to sleep, and then plug in a USB mouse. Your system should wake up...)

So, yes, as long as your UPS will announce a state change, it should be detected.

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I've tried it with my UPS (APC Back-UPS E700) and Mac Pro (2008) I can confirm it does wake the Mac Pro on a power failure when the Mac Pro is asleep. – Steve Folly Dec 29 '09 at 21:12

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