I have long thought computers were analogous. I know there are prevention circuits inside them to protect against surges, I still lean on using sleep rather than power down method.

As to why it would magically turn on, a few things could be the culprit.

First, you need to make sure it is sleeping, it could just be that the monitor has gone to sleep (black screen), but the machine itself is not really asleep. Applications like Entourage are known for preventing a machine from going to sleep if you allow it to check email on a schedule. Any application that does background work can prevent or interfere with sleep.

One workaround and a much more secure way to deal with computers in general, especially laptops, is to set the Security Settings in the System Preferences to “Log out after x minutes of inactivity”. This will gracefully close any and all apps you have running, and take you to the login screen. Your sleep settings will still hold true while at the login screen.

The solution to your issues, assuming you are in fact really sleeping, which you can chose from the Apple Menu and selecting “Sleep”, will be in the Energy Saver Preferences.

Open the System Preferences from the Apple Menu -> System Preferences -> Energy Saver. Make sure that “Wake for Ethernet network access” is not checked. This is used for a feature called “Wake on Demand“, which is very handy in and of itself, but could explain your problems.

If you want this feature on, which many do, you will have to unplug all your 3rd party peripherals such as printers, and add them in one at a time, until you find the device that is kicking your machine into a woken state.

There is a little more data about Wake for Network Administrator Access (Ethernet Only, Wifi does not seem to apply), and Apple also has About Energy Saver sleep and idle modes in Mac OS X.

I would also take off the “Start up automatically after a power failure”, that setting largely being good for servers. Or if you have converted/use your Mac as a movie viewing device connected to your TV and desire it always on.

Also check out the schedule options (also in Energy Saver Preferences), which could be automatically shutting down and then rebooting your machine on some schedule.

Finally, the last thing it could be would be corrupt Power Management Settings (PMU). To reset the PMU, which every mac does it a little different; some require you to open them and press a button; usually the older G4’s are set this way. The PMU controls everything from the sleep, wake, fans, and a lot more. It can get messed up at times.

It also looks like Apple has moved from a PMU to a SMU, or System Management Controller on some systems. You can look at instructions for resetting the SMU on your imac as well.

Oh, one last thing. Many of these settings are stored within internal memory of the computer, but need power in order to maintain the remembering of those settings. This is done with a small battery inside the machine. While most of these batteries last the lifetime of the machine, and often longer, at times, they can go bad or corrode, causing all sorts of erratic behavior.

If you find a corroded battery perhaps due to living in a humid or beach front locale (salty air is a killer), do your best to clean the corrosion off. Radio Shack will sell a circuit board cleaner that is safe for getting on any electronic components. This product comes in a red spray bottle last I looked, and is highly alcohol based, so it can evaporate quickly.

Battery replacement can go a little beyond what the casual user may be interested in performing, I would try the other suggestions first. Some machines need Torx style screwdrivers, which not everyone has on hand.

Here is a pdf from Apple that shows how to do battery replacement on one iMac, though you will have to google for your specific model. Granted, just opening up the iMac, it will be pretty obvious as to where the battery is located at. Replace it, or meter it to make sure it has the marked voltage. Make sure you take note as to the orientation of the battery, it is not always clear, and the markings on the circuit board can sometimes be hard to see. You definitely do not want to put it in backwards.

Most Macs use a 3.6 volt lithium battery

As a final step, reset the PRAM as well, which can often times help clear out any goofy settings that have built up, or become corrupted.

Please come back and let us know what you found out.

You may also want to take a look at our post titled The importance of an uninterruptible power supply

Regards, David Burrell

Incidentally, a Mac mine even consumes less power in sleep, there is no monitor. As near as I can measure it is about 0.1 watts.

It is kinda fun to know how long a Mac desktop has been on.
If you go to “Terminal” and enter: “uptime” (without the ” s and press return, it will tell you how long it has been on. My mini was on over 63 days. Both were Shut Down to install Snow Leopard.

OS X has a few maintenance routines that run on a schedule. If you always shut your machine down, those may not get a chance to run.

On the other hand, sometimes, a clean restart will make your computer work better, as over time it can have applications clog up memory and do other bad things.

In general, it is up to you, you are not going to hurt anything by leaving it running, or shutting it down.

I’ve noticed on my eMac (3rd Rev.) that if I have the volume all the way down in the OS, then reboot, I won’t have a startup “bong” but if I have the volume at any setting above zero I will have the startup sound. I’m not sure if this applies in your situation but I just thought it was worth mentioning.

I personally have not had Time Machine wake a machine up, and had to take steps to keep the machine awake at times to get a full backup.

I would suggest you try telling your machine to “Put the hard drive to sleep when possible” in the Energy Saver prefs. Generally, a spun down drive is pretty hard to have spun back up again unless you wake the machine up.

Rather than shutting off time machine, which you may forget to turn back on, you could unmount your second backup drive, that would make time machine ignore it as well.

There was a time many years ago where you could use your keyboard to start up your computer, and you could hit a 4 key combo and force an immediate reboot.

Those days are gone with USB taking over. Thanks for posting your comment, it could be handy for those who have the correct hardware combination.

A light press of the power button puts it to sleep. I like that feature. Now I know to hold it longer to shut it down.

Also, I was using Word from MacOffice2004 and it froze in the middle of selecting a font. I waited and waited to no avail. So I experimented and held down the ESC key to see what would happen. It terminated Word. I’m hoping that was the correct thing to do. I opened Word back up and everything went smoothly after that.

Thank for putting this together. If I’ve posted this in the wrong area, please let me know.

Seth

I assume your computer can make other sounds?

You did not happen to install some 3rd party tool to change the start up tone volume level?