When HomeKit was first introduced in iOS 8, Apple chose to position the Apple TV at the centre of the system, to act as a hub or gateway for controlling access to HomeKit devices remotely. Without an Apple TV, you could control your HomeKit accessories directly from an iPhone, iPad, or Apple Watch that’s in Wi-Fi or Bluetooth range, but when away from home, you’d have no ability to control or even monitor the status of your HomeKit devices — for that you’ll need a HomeKit hub, which was originally a role limited to the Apple TV. While the third-generation Apple TV originally filled this role — and still can in a limited capacity — the stakes went up with iOS 10 and tvOS 10 last year, leaving the older third-gen model out of the HomeKit party for features like streaming video from HomeKit cameras, running automation routines, and accessing more advanced permissions for your secondary HomeKit users.
Fortunately, with iOS 10 Apple provided another way for users who may not be eager to jump into Apple’s “big screen” ecosystem: If you already have an iPad capable of running iOS 10, you can use that as your home hub instead, as long as it remains at home, powered on, and connected to your Wi-Fi network. Setting this up is as simple as going into the Settings app on your iPad and switching on the option to “Use this iPad as a Home Hub.”
Note that you can have more than one Home Hub in your HomeKit system, so even if you’ve already got an Apple TV already, it can be worth setting up your iPad to act as a Home Hub as well — if you’re only using a third-generation Apple TV, you’ll gain support for the full set of HomeKit automation features, and even if you’ve already got a fourth-generation Apple TV, your iPad can act as a secondary/backup Home Hub, and can be used to provide better coverage if you’ve got Bluetooth-based HomeKit accessories that might be out of range of your Apple TV.