Sleep mode and peripherals

Try these suggestions:

• Make sure your computer’s sleep settings are set the way you want. In Energy Saver preferences, use the slider that controls the computer’s sleep.

Open Energy Saver preferences

Other users may be waking your computer remotely to use its shared resources. If you don’t want this to happen, open Energy Saver preferences and deselect “Wake for network access.”

Open Energy Saver preferences

Bluetooth devices can wake your computer. If you don’t want a Bluetooth keyboard or mouse to be able to wake the computer, open Bluetooth preferences, click Advanced, and then deselect “Allow Bluetooth devices to wake this computer.”

Open Bluetooth preferences

Key presses and mouse or trackpad clicks can wake your computer. If your computer wakes when you’re not present, something may be pressing the mouse button or keyboard.

Applications that access a disk can keep your computer from going to sleep. For example, iTunes accesses your disk to read the songs it plays, and DVD Player accesses the optical disc drive to play movies.

People using shared services on your computer can prevent it from sleeping. For example, they may be using a printer connected to your computer or accessing shared files stored on it. In Sharing preferences, turn off any services you don’t need to use by deselecting the On checkbox next to the service.

Open Sharing preferences

• If Spotlight is indexing your hard disk, your computer won’t go to sleep. Click the Spotlight icon on the right side of the menu bar and check whether it says it’s indexing. Indexing your files can take several hours, depending on the number of files on your computer.
• Malfunctioning USB, FireWire, or Thunderbolt devices may keep your computer from going to sleep. Disconnect your USBUSB, FireWire, and Thunderbolt devices and see if your computer goes to sleep. If it does, reconnect the devices one by one, until you find the one that’s malfunctioning. Contact that device’s manufacturer for more information.
• Some PCI extension cards intentionally prevent a computer from going to sleep. Refer to the documentation that came with your card.

I'm not sure what's waking your iMac during sleep mode. Don't know what apps you have that might be scheduled to wake up your iMac (e.g. Time Machine).

I have a Macbook Pro that I use the same kb and trackpad you have. Both devices in System Preferences/Bluetooth/Advance button have the box checked to allow the device to wake up my Macbook Pro. Both devices work all the time in doing so with no depletion of battery life. These checkboxes need to be checked in order to wake up your iMac assuming there is nothing else set to wake it up. I also close all applications and I don't have any USB drives connected before putting the laptop to sleep. I make sure my Mac Mini is not 'connected' in anyway to my Macbook Pro. The Pro sleeps all night and in the morning I click or press a keyboard key to wake it up. Works 100% of the time.

I think you can discount keyboard and mouse/trackpad devices unless one of them is faulty.

If you eliminate every other possibility, you could always try turning just one off one night, and the other the next (so you've always got one available option for waking the computer) to see if you can isolate the problem.

Good point. Open console.app (easiest way to do that is click on Spotlight and type 'console' and hit return.

Look in 'Diagnostic and Usage Messages'. That should tell you when and what process woke up the Mac.