Can thieves use Bluetooth scanners to detect sleeping MacBooks?

Solution 1:

No, it’s not plausible for thieves to scan for Bluetooth signals to detect sleeping Macs.

For your MacBook (or any device, for that matter) to respond, it must be in discovery mode. This is a mode that answers pairing requests and must be initiated by the user. This is why, in macOS you have to go into Bluetooth settings to do this.

When your MacBook sleeps (lid closed), Bluetooth is turned off. Even Power Nap, which periodically enables WiFi (networking) to check for emails and such. It would make no sense for your laptop to continually broadcast Bluetooth signals while sleeping as this would drain the battery.

Bluetooth is disabled. NOTE: This can be changed in your Bluetooth system preferences, in which you can actually choose to make bluetooth devices power on your computer.

^{Source: What Happens When You Put Mac Laptops to Sleep?}

While it is possible for Bluetooth devices to wake a computer

• your computer would be in listening mode; not transmitting
• The device would need to be already paired to wake it
• It can’t override the closed lid; it won’t go into closed clamshell mode as you need to have power, keyboard and mouse attached.

Thieves are more likely to be watching your actions rather than trying to scan for radio signals when they break into vehicles.

Solution 2:

I want to believe that the answer is no for the reasons that Allan suggested about the Mac having to be in discovery or “pairing” mode.

However, I find myself wondering about the setting “Allow Bluetooth devices to wake this computer” (System Preferences » Bluetooth » Advanced) which is on by default.

That seems like might imply the Mac could be open to receive or check for Bluetooth signals.

On the other hand, the descriptive text in the small print suggests that this only works with keyboards/mice/trackpads which are already paired with the Mac. So maybe it would not work with a Bluetooth scanner.

The biggest problem is that I don't know how these BT scanners really work.

Can anyone say definitively that there is no tool out there can ever detect a Bluetooth signal from a sleeping Mac?

The only way I would feel 100% confident would be if Bluetooth was actually disabled when the Mac goes to sleep.

How would you do that? Well, one way would be with Keyboard Maestro and a macro which triggers when the Mac goes to sleep:

Note that for this to work you must have installed blueutil.

By running /usr/local/bin/blueutil --power 0 --discoverable 0 when your Mac goes to sleep, I would feel 100% confident that no Bluetooth scanner would be able to detect it.

If you regularly use Bluetooth, you could have another Keyboard Maestro macro that runs on wake and does

/usr/local/bin/blueutil --power 1

to turn Bluetooth back on, or

/usr/local/bin/blueutil --power 1 --discoverable 1

to turn Bluetooth on and make it discoverable.

Again, I think Allan’s argument makes sense, but because I don’t know if there are scanners out there which can detect a device which can receive a Bluetooth signal even if it is not paired with that device, I don’t feel like I can make a definitive statement.

Update: Since I wrote this, Allan has expanded his answer with a link to MacEnthusiasts.com which makes it seem even more likely that he is correct. If the Bluetooth really is powered off when the lid is closed, then the Keyboard Maestro macros would be superfluous. However, I know that was not always the case with older versions of macOS and/or Mac hardware, as I used to accidentally have my MacBook wake up in my backpack with the lid closed due to (I believe) a paired Bluetooth device waking it. But maybe my experience is now outdated information.