Using and Calibrating Dynamic Lock in Windows 10 Creators Update

Posted on February 20, 2017 by Rafael Rivera in Windows 10 with 18 Comments

Last week, Paul wrote about Dynamic Lock, a Windows 10 Creators Update feature that locks your Windows PC when it’s separated from a Bluetooth-paired phone. But some readers had questions about how Dynamic Lock really works. So I naturally took it apart to answer those questions.

Let’s jump right in.

Hello and Goodbye

As you may remember, Windows Hello is a password-free sign-in experience that unlocks your Windows PC using your face, fingerprint or companion device. It can also be used to authenticate with Windows Hello-enabled apps and websites, and is available in Windows 10 today.

Conversely, in Creators Update, a new Dynamic Lock sign-out experience is coming. This feature figures out if you’re there or not and automatically locks your Windows PC in your absence.

Fun fact: This feature is internally known as Windows Goodbye and in some OEM circles as Proximity Lock. This is the name Microsoft assigned the feature at its WinHEC conference last year, but as far as we know, that name has been retired.

Dynamic Lock

As mentioned earlier, Dynamic Lock automatically locks your Windows PC when you’re not present based on the proximity of a Bluetooth-paired phone. (It may work with other devices, but the intent is phone-only right now. Consider yourself lucky if you get this feature working with a non-phone.)

If you have multiple phones paired with your PC, all of them are considered. That is, either phone will lock your PC if they stray too far. (I suspect this will be configurable via policy, if not end-user UI, in later builds.)

But How Far Is Too Far?

Dynamic Lock determines you’re missing in action by performing the following ritual several times a minute:

  1. Connect to the Bluetooth-paired phone
  2. Retrieve the average Received Signal Strength Indication (RSSI) for that connection
  3. Disconnect from the Bluetooth-paired phone
  4. Determine if the RSSI value dips below a certain threshold

Because an active connection is established every time this ritual is performed, you can bet there will be a battery life hit on both devices. It’s a win-win!

What’s The Threshold?

The threshold, by default, appears to be around -10 decibels (dB). That is, 10dB below the Golden Received Power Range — the sweet spot specific to your particular Bluetooth controller — represented at the 0dB point.

But in my apartment, a 10dB difference means walking halfway across the floorplan before my PC locks. I halved my value to shorten that distance.

To configure this delta yourself, first create the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\NaAuth key. Then create the BluetoothRssiMaxDelta DWORD registry value and set it appropriately (see below). Be sure to lock and unlock your PC to reset Dynamic Lock and commit your changes.

Figuring Out The Right Threshold Value

Setting the correct threshold value is the trickiest part of using this feature.

I couldn’t find any Windows software that retrieved RSSI values correctly, so I threw together a tool for you. It iterates the paired Bluetooth device list and retrieves the most recent signal strength value in a loop. It has a weird sounding name (based on dinosaur genera) and doesn’t handle unreachable devices correctly (thanks to iffy Windows APIs) but it gets the job done. You can find its source code on Gitlab. Pull requests are welcome.

To get the threshold value using the tool, do the following:

  1. Place your phone on your desk/near the PC
  2. Turn on Bluetooth and pair with the PC
  3. Start my tool
  4. The initial signal strength readout for the phone should be somewhere around -10dB or above. (Your mileage may vary.) Scribble this value down.
  5. Now move the phone to a distant location and wait for the app to update
  6. Let the app loop a few times then scribble down the new signal strength value.
  7. Subtract the two numbers, drop the sign, and stuff that value into the registry (see above). Be sure to lock and unlock your PC for the changes to take effect.

It’s hard to guarantee that any of this will work for you, though. There are a bunch of environmental and device specific variables that need to be accounted for. And between you and I, it’s this pickiness that has me wondering if this feature will get cut prior to the general availability of Creators Update.

I’ll keep an eye on Dynamic Lock as we get closer to the completion of Creators Update. If anything changes, I’ll let you know.

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Comments (18)

18 responses to “Using and Calibrating Dynamic Lock in Windows 10 Creators Update”

  1. Avatar

    rpl1

    Two comments really. Distance is one thing, but why do I have to wait 60 seconds? 5 is long enough. Besides Hello logs you in very quickly. Can you tell us how to do this?


    Second was one of my devices that I saw showing on your scanner. I have a Brydge 12.3 that I use when I'm at home. It was showing as currently connected and a signal strength of -74db. The Brydge must have one of the most powerful and efficient Bluetooth radios in existence because, to my knowledge, it's currently 38 miles away and switched off.

  2. Avatar

    anothercalifornian

    Mine stopped locking. Everything in place and set, paired, hello and regedit key. I unpaired, re-pared, checked settings again. Shut off phone. Restarted phone but no lock during this process. Walked away, came back nada...


    version Windows 10 Pro (Domain) laptop (Surface Pro 4) 1709 Build 16299.192


    I cannot see anything else to 'fix'.


    Stumped.

  3. Avatar

    JohnnyCash12

    I love the technical depth of this article. Please keep this type of insight coming.

  4. Avatar

    anothercalifornian

    So if the phone was 0 nearby and -5 when going down to the next floor and -2 would the value for the key be a negative 2? Or perhaps a -5 to mean I've made it 1 floor down?

  5. Avatar

    jboman32768

    That's some pretty comprehensive investigation there, nice work. ?

  6. Avatar

    madthinus

    The word computer / device is missing in the first sentence of the article.

  7. Avatar

    psutherland

    Thanks Rafael, that's great to know!

  8. Avatar

    Chris_Kez

    Thanks Rafael; please contribute more articles!

  9. Avatar

    lwetzel

    "To configure this delta yourself, first create the HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionNaAuth key. Then create the BluetoothRssiMaxDelta DWORD registry value and set it appropriately."

    What is appropriate value. 

    "I couldn’t find any Windows software that retrieved RSSI values correctly, so I threw together a tool for you. It iterates the paired Bluetooth device list and retrieves the most recent signal strength value in a loop. It has a weird sounding name (based on dinosaur genera) and doesn’t handle unreachable devices correctly (thanks to iffy Windows APIs) but it gets the job done. You can find its source code on Gitlab. Pull requests are welcome."

    Both links take me (at least in Edge) just say "waiting for response from" and are blank.

    Am I missing something?


  10. Avatar

    Lewk

    It begs the question, why does it have to be device based at all??

    Why can't there be a timer feature like on mobile phones. On Windows 10 Mobile, the feature is called "Require Sign-In" and has a list of different intervals that Windows waits until it automatically locks the device. On Windows 10 Desktop, the exact same feature of "Require Sign-In" is available, but is limited to two, very useless options of 'Never' and 'Wake on sleep'.

    Screenshots: Mobile and Desktop

    Why not just let us be able to have our computers lock at a specified inactive time-limit just like mobile??

    • Avatar

      crfonseca

      In reply to Lewk:

      Windows has had a "timeout" lock since pretty much forever, this is a different thing.

      It might not work so well yet, but I believe the idea is to have the PC lock as soon as your phone, or, indeed, any bluetooth device, something like a fitness band would work too, is at a certain distance from it.

      That said, maybe Microsoft should move the screen saver settings to the Settings app, because currently that thing is a mess.

      Oh, and they're doing this: New Require sign-in settings.

    • Avatar

      Rafael Rivera

      In reply to Lewk:

      Screen Saver Settings > On resume, display logon screen

      • Avatar

        Jacob Klein

        In reply to Rafael Rivera:


        Yep. What I typically do is:

        -- Set the display to turn off after 2 minutes

        -- Set the screen saver to "Start Blank" after waiting 3 minutes, with "On resume, display logon screen" checked.

        Note: I don't use sleep or hibernate, because my PCs do distributed computing 24/7.

        Note 2: This method of locking is in an interface that really needs to be simplified and cleaned up. Come on Microsoft! :)

  11. Avatar

    seamussmith

    Does this still work for calibrating? And does it work in normal releases or only creator?

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