A closed lid should mean sleep
When you close a MacBook's lid, it normally goes to sleep within moments: the screen turns off, apps pause and the chip all but stops. A sleeping Mac makes very little heat, so it should feel close to room temperature after a while.
There are a few honest exceptions:
- An external display. With a display, keyboard and power connected, a closed MacBook keeps running on the big screen. That's on purpose, and it's warm because it's working.
- Brief check-ins. With Power Nap on, a sleeping Mac wakes briefly to fetch mail, calendar and iCloud updates. That's short and shouldn't make it hot.
- Something that won't let it sleep. An app, a download, a backup or an update can hold the Mac awake with the lid closed. That's the usual reason for a hot bag.
Find what's keeping it awake
In Activity Monitor
- Open Activity Monitor (Command-Space, then type its name).
- Click Energy.
- If you don't see a Preventing Sleep column, choose View › Columns and turn it on.
- Anything marked Yes is holding your Mac awake right now. If it's an app you recognize, let it finish or quit it before you pack up.
In Terminal, for the full picture
Open Terminal and run:
pmset -g assertions
It lists everything currently asking macOS to stay awake, with the app or process behind each request. Lines such as PreventUserIdleSystemSleep or PreventSystemSleep with a value of 1 are the ones that matter; the processes listed below them are the ones asking. This only reads information; it changes nothing.
Settings that wake it
On a MacBook, open System Settings › Battery and click Options:
- Power Nap lets a sleeping Mac check for mail, calendar and iCloud updates. Its menu lets you choose when that's allowed, or turn it off. If heat in your bag worries you, don't allow it on battery.
- Wake for network access lets a sleeping Mac wake to share things like printers or music on your network. Most people don't need it on a laptop.
Bluetooth devices and anything plugged in can wake a Mac too. If your Mac keeps waking in your bag, unplug accessories before you close the lid.
Before it goes in your bag
- Make sure it's asleep. Close the lid and wait a few seconds. If you've just started a big download, backup or update, let it finish first.
- Don't pack it mid-update. Updates can keep a Mac busy for a long time.
- Shut it down for long trips. A Mac that's off can't wake up in your bag.
- Keep it out of hot places. Apple advises against leaving a Mac laptop in a parked car, where temperatures can go well beyond the 10° to 35° C (50° to 95° F) Apple recommends.
If your Mac gets hot in your bag again and again with nothing preventing sleep, contact Apple.