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I have a Dell Inspiron 1525 laptop, about three years of age. Usually I suspend it (put into sleep) in the evening and resume in the morning. Recently the laptop started turning on by itself during the night — not to mention that this always happens at about the same time!

The internet (e.g., this question) mainly suggests turning off Wake-On-LAN for the Ethernet card (I've long had it disabled through ethtool, let alone that there's no cable plugged in), or inspecting scheduled tasks. But I use GNU/Linux (kernel version 3.1.7, x86-64 arch), so the second option also doesn't seem plausible. The BIOS is at the latest version. I've checked the package manager logs and there were no suspicious/interesting changes during the period when this started happening.

Having spent some time looking into the problem online, I dare not ask for a ready solution, but for at least a suggestion of what could be wrong, and if this is likely to be a software or a harware problem. I imagine that it could be due to dust or partially broken/bent wires causing a short circuit and a pulse somewhere on the power button or other reset lines; but a software problem seems possible as well.

UPDATE: Thanks for the suggestions. Some additional info:

  • dmesg has no suspicious lines
  • The BIOS does not have (or show) any resume-on-alarm settings
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This does not sounds like a problem to me, more like a feature gone rouge. Not sure how to track it down though. – soandos Jan 8 '12 at 9:34
I've seen pcs/laptops do his due to static electricity and noise bursts in the power lines – stijn Jan 8 '12 at 9:45
For the record, my laptop turns ON on its own because of a setting that makes it go from sleep to hibernation after X hours of sleep. Creepy when it wakes you up. Probably not your problem, though, since it would be still asleep/hibernating afterwards. – Joanis Jan 8 '12 at 12:24
Maybe look through the kernel logs and see how the computer is woken up? – Jan 8 '12 at 14:08
Hi it is strange, I have a HP desktop computer with Win7 and it also sometimes resumes from hibernation just few seconds after shutting down or sometimes without any reason during the day or night when I am not in the office. I noticed this after some OS update, after another one this problem vanished but after another update it is here again. Funny... – Juhele Jan 8 '12 at 16:15

My first thought is to check the BIOS settings for any kind of auto on setting. Most have a way of turning themselves on at a certain time of day, this may have been enabled. You could also go into BIOS and set defaults and reboot to see if the alleviates the problem as well.

As for less likely possibilities, like you said it could be a short in any of the circuits for power or reset switches, but also something in the keyboard as well since tapping a key on the keyboard will also wake up a sleeping computer.

The last thing that comes to mind is some really funky power issues. Spikes or sags in power can do some really weird stuff to computer equipment.

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As @Paperlantern says, many BIOSes have a "power-on-at-a-certain-time" feature. I'm certain it is this, especially if it reliably happens at the same time each day.

If your BIOS does not have such an option, it's unlikely but possible the BIOS and embedded controller in your system support this feature, but it was just made inaccessible from the Dell BIOS menu by Dell. If the battery in your laptop is going out, or if a program messed with the CMOS NVRAM, the right bits may have been flipped to enable this. You might try updating your BIOS. If the battery is easily accessible (not sure about that specific model) you might try removing all power, removing the CR2032 battery, waiting about 15 minutes, and then replacing/reassembling and then go into your BIOS and configure it as you need.

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I addition to @Paperlantern's suggestion and despite your use of ethtool, I would check your BIOS settings for Wake-on-Lan or Wake-on-device behavior. I'd alos check to see wheter your laptop provides a USB power bypass (not sure that's the right name for it) - basically allowing you to charge and use USB devices even when the main OS is off.

Finally, I'd check and see whether your laptop came preinstalled with one of those tiny InstantOn OSs - they might have something defined in them (or the BIOS again) prompting the machine to turn on for updates etc.

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up vote 0 down vote accepted

The problem disappeared after I replaced the old laptop battery with a new one. The old battery didn't have much capacity left (sorry for not mentioning, this didn't seem relevant). I presume that, when the charge level went below a certain threshold, the BIOS woke up the OS to take action (shut down or hibernate).

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Perhaps the Bluetooth receiver stays awake and a device tries to connect to it. Try turning of the Bluetooth on the laptop.
I have the same issue, and am testing this out at the moment after seeing it being mentioned in the eventviewer logs.

Also see this question: How can I prevent my computer from waking up accidentally? (Which is what is happening to me)

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