Why your PC turned on by itself

What can wake a PC

A computer that is off is not entirely off: a few parts stay powered precisely so it can be turned back on. Windows calls the piece that started it the "wake source", and records its name every time the PC comes back from sleep. There are three possible sources.

The network card

It is the same one that turns the PC on by voice: it answers a special packet, the "magic packet", and starts the machine. Many cards, though, ship with a wider permission — they wake up for any packet that reaches the computer. On a network with a router, a printer, a TV and a few phones, packets fly at all hours: there is your three-in-the-morning start-up. The good news is that the narrow permission — "magic packet only" — is a single checkbox, and the voice command keeps working exactly as before.

Windows wake timers

Windows lets a scheduled task turn the computer back on to do its job: updates, nightly maintenance, a backup program that runs at fixed times. They are useful, but nobody ever introduced them to you: you find out only when the PC starts up on its own at the same time every night. Each task has its own switch, and they come off one at a time — never all at once.

The mouse, the keyboard, the power button

A mouse nudged by the cat, or a key brushed by accident, is enough to wake most PCs. Windows records "fixed feature" or the device name in that case, and SayBoot tells you "by someone at the PC". If it happens often, the permission comes off the same way as the network card's, in the mouse's or keyboard's properties.

How to read it in SayBoot

When SayBoot has recorded the power-on, the computer's card carries a "Last power-on" line: it says when the PC turned on and who did it — you by voice, a schedule, or "on its own" with the source Windows recorded. Tapping it opens the list of recent power-ons, so a pattern (always 03:12, always the network card) shows at a glance.

When a power-on is "on its own", the line carries an explanation of what it was and a pointer to this page. If you have notifications on, the same information reaches your phone as it happens.

Taking the wide permission away from the network card

The goal is to keep waking on a magic packet — the one SayBoot uses — and to switch off waking on any traffic. You need administrator rights.

1. Press the Windows key, type Device Manager and open it. Expand Network adapters and double-click the one the PC is connected through (usually the one with "Ethernet" in its name: Wi-Fi hardly ever starts a computer that is off).

2. Go to the Power Management tab. Leave "Allow this device to wake the computer" ticked, and tick the one below it, "Only allow a magic packet to wake the computer".

3. Confirm with OK. No restart needed. Try the voice command right away: it must work exactly as before.

Taking the permission away from a scheduled task

First find out which one it is. Open the Command Prompt (or Terminal) and type:

The answer lists the timers allowed to turn the computer back on, with the name of the task that asked for it. SayBoot already gives you the same name in the "Last power-on" line, whenever Windows recorded it.

1. Press the Windows key, type Task Scheduler and open it. In the tree on the left follow the path of the task you found, then select it in the middle list.

2. Open its properties (double-click) and go to the Conditions tab. Untick "Wake the computer to run this task".

3. Confirm with OK. The task will still run, but only while the computer is already on.

What Windows does not record

One honest limit: if the PC was off or hibernated, Windows does not record who turned it on. A wake source exists only when the computer comes back from sleep. In those cases SayBoot writes "unknown origin" instead of guessing, and sends no "turned on by itself" notification.

A second limit: Windows says the network card did it, but not whether it was any old packet or a magic packet sent by another program or another device on your network. If the PC keeps starting up on its own through the network after you have narrowed the permission, it is almost certainly something sending magic packets at home: another computer, a network app, the router.

Shut down, sleep or hibernate?

If it is a desktop you use every day, the advice is sleep: it comes back in an instant, it draws a few watts, and it is the only state in which Windows records what woke the machine — so the "Last power-on" line works at its best exactly from here.

If instead the computer sits untouched for days — a week away, a machine you switch on now and then — hibernate or shut it down. In that case Windows records nothing about who turned it on, so the origin cannot be known; the app still says "by you" whenever the power-on was one you asked for, by voice or from the app.

Microsoft gives the same advice: sleep for short breaks, hibernate when a laptop on battery is left alone for a long stretch. About shutting down it says nothing either way.

Hibernate and off, as you can see, draw almost the same: in both cases the network card stays powered, and it is the card that keeps the voice power-on possible.

On the bill the gap is small. Sleep costs between 1 and 5 W more than hibernate, roughly 1–3 kWh a month: at about $0.15–0.20 per kWh in the United States that is around $0.15–0.60 a month, and at about £0.25–0.30 per kWh in the United Kingdom around £0.25–0.90 a month.

A note on fast startup

With fast startup enabled, "Shut down" does not really switch everything off: Windows hibernates the system kernel so it can start again faster. On some network cards that has a known side effect — waking over the network after a "Shut down" does not work, while after a "Restart" it does.

If the Alexa power-on fails only after a shutdown, try turning it off: Control Panel → Power Options → Choose what the power buttons do → Change settings that are currently unavailable, then untick "Turn on fast startup (recommended)" and save. The PC takes a few seconds longer to boot, and in exchange it answers the network even when it is off.

Windows and Microsoft are trademarks of Microsoft Corporation. Alexa, Amazon and Echo are trademarks of Amazon.com, Inc. or its affiliates. SayBoot is an independent application and is not affiliated with, endorsed or sponsored by them.