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I have had this problem for a long time now, but i've never taken the time to really investigate it.

So i have this mid-2007 24-inch C2D iMac. I like to keep the machine running all the time, but i have the display only (not the entire machine) set to go to sleep after a few minutes.

For the most part this works fine, but specific types of network activity will wake the display. I think there are a number of other things that can do it, but i know the following will for sure wake the display, 100% of the time:

  • Connecting to IRC from any other Mac or Windows PC on the network
  • Connecting to IRC from my iPhone
  • Associating a device with the wireless network (which happens with my phone every day when i come home from work)

The obvious thing to check of course is the 'wake for network access' feature in Energy Saver. This is not enabled now, nor has it ever been.

I have also checked Console for any 'wake' entries, but i don't see any. I assume these only appear when the machine itself wakes up, not just when the display comes on.

I have confirmed that when the iMac's WiFi connection is disabled, the wake-ups do not occur. The iMac doesn't use wired Ethernet, nor do any of the other devices (all are on WiFi).

The problem has persisted across multiple clean installations (not upgrades) of Leopard, Snow Leopard, and Lion. It did not occur with my Windows netbook (which i just recently got rid of), but i haven't been able to verify whether it occurs with my Macbook Air.

It has also persisted across two different routers.

... And one bizarre thing that occurred to me as i writing that is this:

My current router has simultaneous dual-band, so there is a 5 GHz N network and a separate 2.4 GHz G/N network. My iMac and Macbook Air are both on the 5 GHz network, but the iPhone doesn't support that frequency, so it connects to the 2.4 GHz network. That means that the iPhone connecting to the 2.4 GHz network is somehow waking the iMac on the 5 GHz network, which blows my mind.

(The previous router was 2.4 GHz only, so they were all on the same network. But both routers have used Tomato, so i suppose that could be a connection.)

Any ideas? :|

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there is an article here on the apple helpsite that may be of help, it decribes various instances when wake on demand can be used to wake your Mac, so I am not sure if they have any of these options enabled. There is a lot more info on the article but here is a sample of some of it :

iTunes Sharing

Applications such as iTunes allow you to share your music and movies with friends and family on your local network. Wake on Demand allows for your Macs to go to sleep, but wake up automatically to let family view your shared stuff.

Printer Sharing

In Mac OS X, you can connect a printer to a Mac and share it with other computers on the network. Wake on Demand allows for that Mac to go to sleep while idle, but wake up automatically when needed to handle a print job.

Back to My Mac

With Wake on Demand, you can access your Mac at home using Back to My Mac, even if your Mac is set to sleep.

Local File Sharing, Screen Sharing, other sharing services

In addition to helping your home Mac wake when you remotely access it using Back to My Mac, Wake on Demand also provides the same capability when you access your Mac locally from within your own home network, whether for File Sharing, Screen Sharing, remote login via SSH, or other sharing services.

http://support.apple.com/kb/HT3774

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