Apple Watch Unlock, 802.11ac, and Time

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One of the benefits of upgrading to MacOS 10.12 Sierra is the ability to unlock my Mac laptop with my Apple Watch. Yet I’m not able to do that. Why? Turns out, the answer involves some pretty cool tech.

Somebody’s Watching You

The tech specs list the 2013 MacBook and higher as the minimum model needed to enable Watch Unlock on your Mac. You also need a few other things, like Bluetooth enabled and a Watch running WatchOS 3. I checked my personal MacBook against the original specs and found everything in order. I installed Sierra and updated all my other devices and even enabled iCloud Two-Factor Authentication to be sure. Yet, when I checked the Security and Privacy section, I didn’t see the checkbox for the Watch Unlock to be enabled. What gives?

It turns out that Apple quietly modified the minimum specs during the Sierra beta period. Instead of early 2013 MacBooks being support, the shift moved support to mid-2013 MacBooks instead. I checked the spec sheets and mine is almost identical. The RAM, drive, and other features are the same. Why does Watch Unlock work on those Macs and not mine? The answer, it appears, is wireless.

Now AC The Light

The mid-2013 MacBook introduced Apple’s first 802.11ac wireless chipset. That was the major reason to upgrade over the earlier models. The Airport Extreme also supported 11ac starting in mid-2013 to increase speeds to more than 500Mbps transfer rates, or Wave 1 speeds.

While the majority of the communication that the Apple Watch uses with your phone and your MacBook is via Bluetooth, it’s not the only way it communicates. The Apple Watch has a built-in wireless radio as well. It’s a 2.4GHz b/g/n radio. Normally, the 11ac card on the MacBook can’t talk to the Watch directly because of the frequency mismatch. But the 11ac card in the 2013 MacBook enables a different protocol that is the basis for the unlocking feature.

802.11v has been used for a while as a fast roaming feature for mobile devices. Support for it has been spotty before wider adoption of 802.11ac Wave 1 access points. 802.11v allows client devices to exchange information about network topology. 11v also allows for clients to measure network latency information by timing the arrival of packets. That means that a client can ping an access point or another client and get a precise timestamp of the arrival of that packet. This can be used for a variety of things, most commonly location services.

Time Is On Your Side

The 802.11v timestamp has been proposed to be used as a “time of flight” calculation all the back since 2008. Apple has decided to use Time of Flight as a security mechanism for the Watch Unlock feature. Rather than just assume that the Watch is in range because it’s communicating over Bluetooth, Apple wanted to increase the security of the Watch/Mac connection. When the Mac detects that the Watch is within 3 meters of the Mac it is connected to via Handoff it is in the right range to trigger an unlock. This is where the 11ac card works magic.

When the Watch sends a Bluetooth signal to trigger the unlock, the Mac sends an additional 802.11v request to the watch via wireless. This request is then timed for arrival. Since the Mac knows the watch has to be within 3 meters, the timestamp on the packet has a very tight tolerance for delay. If the delay is within the acceptable parameters, the Watch unlock request is approved and your Mac is unlocked. If there is more than the acceptable deviation, such as when used via a Bluetooth repeater or some other kind of nefarious mechanism, the unlock request will fail because the system realizes the Watch is outside the “safe” zone for unlocking the Mac.

Why does the Mac require an 802.11ac card for 802.11v support? The simple answer is because the Broadcom BCM43xx card in the early 2013 MacBooks and before doesn’t support the 802.11v time stamp field (page 5). Without support for the timestamp field, the 802.11v Time of Flight packet won’t work. The newer Broadcom 802.11ac compliant BCM43xx card in the mid-2013 MacBooks does support the time stamp field, thus allowing the security measure to work.


Tom’s Take

All cool tech needs a minimum supported level. No one could have guess 3-4 years ago that Apple would need support for 802.11v time stamp fields in their laptop Airport cards. So when they finally implemented it in mid-2013 with the 802.11ac refresh, they created a boundary for support for a feature on a device that was in the early development stages. Am I disappointed that my Mac doesn’t support watch unlock? Yes. But I also understand why now that I’ve done the research. Unforeseen consequences of adoption decisions really can reach far into the future. But the technology that Apple is building into their security platform is cool no matter whether it’s support on my devices or not.

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Are We The Problem With Wearables?

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Something, Something, Apple Watch.

Oh, yeah. There needs to be substance in a wearable blog post. Not just product names.

Wearables are the next big product category that is driving innovation. The advances being made in screen clarity, battery life, and component miniaturization are being felt across the rest of the device market. I doubt Apple would have been able to make the new Macbook logic board as small as it is without a few things learned from trying to cram transistors into a watch case. But, are we the people sending the wrong messages about wearable technology?

The Little Computer That Could

If you look at the biggest driving factor behind technology today, it comes down to size. Technology companies are making things smaller and lighter with every iteration. If the words thinnest and lightest don’t appear in your presentation at least twice then you aren’t on the cutting edge. But is this drive because tech companies want to make things tiny? Or is it more that consumers are driving them that way?

Yes, people the world over are now complaining that technology should have other attributes besides size and weight. A large contingent says that battery life is now more important than anything else. But would you be okay with lugging around an extra pound of weight that equates to four more hours of typing time? Would you give up your 13-inch laptop in favor of a 17-inch model if the battery life were doubled?

People send mixed signals about the size and shape of technology all the time. We want it fast, small, light, powerful, and with the ability to run forever. Tech companies give us as much as they can, but tradeoffs must be made. Light and powerful usually means horrible battery life. Great battery life and low weight often means terrible performance. No consumer has ever said, “This product is exactly what I wanted with regards to battery, power, weight, and price.”

Where Wearables Dare

As Jonny Ive said this week, “The keyboard dictated the size of the new Macbook.” He’s absolutely right. Laptops and Desktops have a minimum size that is dictated by the screen and keyboard. Has anyone tried typing on a keyboard cover for and iPad? How about an iPad Mini cover? It’s a miserable experience, even if you don’t have sausage fingers like me. When the size of the device dictates the keyboard, you are forced to make compromises that impact user experience.

With wearables, the bar shifts away from input to usability. No wearable watch has a keyboard, virtual or otherwise. Instead, voice control is the input method. Spoken words drive communication beyond navigation. For some applications, like phone calls and text messages, this is preferred. But I can’t imagine typing a whole blog post or coding on a watch. Nor should I. The wearable category is not designed for hard-core computing use.

That’s where we’re getting it wrong. Google Glass was never designed to replace a laptop. Apple Watch isn’t going to replace an iPhone, let alone an iMac. Wearable devices augment our technology workflows instead of displacing them. Those fancy monocles you see in sci-fi movies aren’t the entire computer. They are just an interface to a larger processor on the back end. Trying to shrink a laptop to the size of a silver dollar is impossible. If it were, we’d have that by now.

Wearables are designed to give you information at a glance. Google Glass allows you to see notifications easily and access information. Smart watches are designed to give notifications and quick, digestible snippets of need-to-know information. Yes, you do have a phone for that kind of thing. But my friend Colin McNamara said it best:

I can glance at my watch and get a notification without getting sucked into my phone


Tom’s Take

That’s what makes the wearable market so important. It’s not having the processing power of a Cray supercomputer on your arm or attached to your head. It’s having that power available when you need it, yet having the control to get information you need without other distractions. Wearables free you up to do other things. Like building or creating or simply just paying attention to something. Wearables make technology unobtrusive, whether it’s a quick text message or tracking the number of steps you’ve taken today. Sci-Fi is filled with pictures of amazing technology all designed to do one thing – let us be human beings. We drive the direction of product development. Instead of crying for lighter, faster, and longer all the time, we should instead focus on building the right interface for what we need and tell the manufacturers to build around that.