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Does anyone know how the Apple Watch unlock feature work in macOS Sierra?

I figured out, that I have to be very near my Mac, that the feature works.

Does it use Bluetooth (BLE) or WIFI?

It would be really nice to get some details about this nice feature.

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3 Answers 3

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It uses both Bluetooth LE 4.0 AND 802.11ac WiFi.

Bluetooth is used to discover the Apple Watch and establish a connection.

Then it uses WiFi to do "time-in-flight" calculations - i.e. to figure out how far your watch is from the Mac. The Mac needs to support 802.11ac WiFi for this to work. All watches are supported, both the old and the new - even though the old ones does not support 802.11ac.

This way it is possible to prevent attacks such as someone planting a "bluetooth repeater" near you, so that it could replay your bluetooth responses captured this way to a Mac located somewhere remotely.

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  • The timing packets are likely encrypted as well or at least the time stamps are encrypted to prevent playback attacks where someone captures the traffic that unlocked the Mac today at 8 am and then tries to replay it tomorrow when you and your watch are not present.
    – bmike ♦
    Commented Oct 4, 2016 at 11:11
  • The first-generation Apple Watch does not have 802.11ac.
    – At0micMutex
    Commented Oct 4, 2016 at 12:23
  • Does apple provide any official docs?
    – patrickS
    Commented Oct 4, 2016 at 12:49
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    You can hear Phil Schiller/Craigh Federighi explain the implementation here: vimeo.com/171186055#t=40m15s
    – jksoegaard
    Commented Oct 4, 2016 at 13:07
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    Also a nice article: networkingnerd.net/2016/09/21/…
    – patrickS
    Commented Oct 21, 2016 at 5:59
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I found a interesting article, where this feature is described in detail:

https://networkingnerd.net/2016/09/21/apple-watch-unlock-802-11ac-and-time/

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  • Pls add details to your article so that it answers the question even if the link is broken or the material in it is changed.
    – Alper
    Commented Aug 9, 2023 at 14:36
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It uses both WIFI.

WIFI checks if your connected to the same network to 'grant you access'.

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    If you take a look at vimeo.com/171186055#t=40m15s - Craigh Federighi explains that the distance measurement is done via WiFi - not Bluetooth.
    – jksoegaard
    Commented Oct 4, 2016 at 13:08
  • Would upvote if you update (and I notice)
    – mcint
    Commented Jul 28, 2023 at 22:45

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