If you are venturing the wonderful world of HomeKit, you may have noticed that some of your devices cannot be controlled or viewed while out and about. This is where HomeKit hubs come into play. A HomeKit hub acts as a relay to your accessories through iCloud, allowing you to turn on and off your lights, even when you are off your home Wi-Fi network. Here's everything you need to know about how it all works.

So what does a HomeKit hub do for HomeKit, anyway?

By default, HomeKit is limited to your personal Wi-Fi network: All handshaking and Siri commanding happens within those boundaries. But a HomeKit hub — in combination with your Apple ID — gives your iPhone, iPad, or Mac, a way to securely talk to your HomeKit devices even when you're outside the house.

Which devices act as a HomeKit hub?

There are several Apple devices that can act as a hub for your HomeKit setup. Apple TV (3rd generation or later), HomePod, and iPads running iOS 9 or above. The 3rd generation Apple TV is somewhat limited when it comes to HomeKit as it cannot share access to your accessories outside of the home to other users and it does not support camera video streams.

How does a HomeKit hub connect to my accessories?

It's an under-the-hood mixture of iCloud Keychain and HomeKit frameworks. Say you're on LTE: You press the Home button to pull up Siri and give the command "Turn on the lights." Without a HomeKit hub, that command goes nowhere — Siri replies with "I can't do that."

With a HomeKit hub on your home Wi-Fi network, however, that command travels over your cellular network back to your hub, where it handshakes with your Apple ID. "This is the owner of this HomeKit network," the HomeKit hub says to your accessories. "Here's a command from them." The accessories execute the command, and the lights in your home pop on.

Now, if you're doing this on LTE sitting in front of your lights, you're going to see a slight delay between giving Siri the command and the command actually happening: This is because of that extra handshake that happens between the HomeKit hub and the accessory; normally, when you're on Wi-Fi, your commands go directly to the accessory or bridge that controls the accessory.

But seeing that 90 percent of commands given outside your Wi-Fi network won't be to turn on a light right in front of you; they're going to be to unlock your door, turn up the thermostat, or turn on the lights from your car. By the time you get to your door, the command should have been executed with time to spare.

So it's just an extender? Why can't my HomeKit hub be a HomeKit bridge and talk to my non-HomeKit accessories like my Nest?

Just because your Apple TV can talk to HomeKit doesn't mean it can link your Hue bulbs and Nest thermostat into that framework. This is due to the various methods of connectivity protocols that some devices employ. The current set of HomeKit hubs, Apple TV, HomePod and the iPad only support Bluetooth and Wi-Fi. Devices such as the Philips Hue line of lighting use a wireless protocol called Zigbee which requires specific hardware radios. On top of that, for the box to be a HomeKit bridge, it would need to develop secure handshakes and APIs for every third-party accessory out there — no easy feat.

We are not saying that there's never going to be a future HomeKit hub that also acts as a HomeKit bridge, but such a thing is technically not possible currently for devices due to the various networking protocols. So we're stuck with bridges from the various manufacturers for the time being.

How do I set up a HomeKit hub in my home?

Setting up a HomeKit hub is pretty simple. Typically it involves signing into the same iCloud account that your HomeKit home is set up with and toggling on the HomeKit hub option. For detailed steps on this process, check out our guide below.

How to make your Apple TV, iPad, or HomePod a Home Hub

Any other questions?

Anything else about HomeKit hubs and HomeKit you're confused about? Let us know in the comments, we will be glad to answer any questions that you may have.

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Updated August 2019: Updated available hubs.

Serenity Caldwell contributed to an earlier version of this guide.