Hello and a very warm welcome to the forum.
I understand that you already have an Apple Home Hub, which serves as a Thread Border Router and Matter Controller.
If you add the M3 Hub, both will form a shared Thread network, provided you use the Aqara Home app to import the existing Thread network credentials into the M3. Regarding your question about the communication path:
- Inside the Thread Mesh: Your sensors don’t communicate with a specific hub. Instead, they route their data packets automatically via the best available nodes within the mesh. The mesh itself handles the routing dynamically, ensuring the most stable path to the infrastructure. The M3 Hub will therefore strengthen your Thread network.
- The Hubs as Border Routers: The Apple Hub and the Aqara M3 act as gateways (Border Routers). They translate the Thread traffic into standard IPv6 data for your home network (LAN/Wi-Fi).
- Backbone Coordination: Both hubs are coordinate over the so-called “Thread Backbone Link.” This is a non-Thread IPv6 network—typically Ethernet or Wi-Fi—that connects multiple Thread Border Routers to synchronize data and extend network range. Only if two parts of your Thread mesh are too far apart to communicate directly via radio, the Border Routers will automatically route the traffic over your Wi-Fi/Ethernet backbone instead. This ensures a stable connection across different floors or through thick walls, as long as both hubs are connected to your home network.
Ultimately, you don’t need to worry about the specific communication paths. Thread is designed to automatically manages the routing and always finds the most efficient and reliable path for your data.
The M3 Hub and the Apple Home Hub both also function as Matter Controllers. The M3 Hub acts as the Matter Controller for Aqara Home, and the Apple Home Hub for Apple Home. For every ecosystem where you want to add a Matter device, you need a Matter Controller from that specific manufacturer. For example, if you also wanted to add devices to Google Home, you would additionally need a Nest Hub.
Further reading: Matter & Thread: A Guide Through the Jungle
Yes, if the sensors are already bound to the Apple Home Hub via Matter over Thread, selecting “Turn On Pairing Mode” will generate a new Matter Multi-Admin code. You can then use this code to add the device to the M3 Hub as a second controller. Please note that names or room assignments changed in one app will not automatically sync to the other.
Yes, with the Aqara M3 Hub, you get a native alarm system where you can utilize these accessories. You must configure the alarm system within the Aqara app, but you can still activate or deactivate the respective alarm modes directly in Apple Home. A major advantage of using the M3 as the controller for these scenarios is local execution: the alarm will still trigger even if your internet connection is down or the Apple Home Hub is offline, providing significantly higher reliability for your security setup. However, as far as I know, the alarm system is provided via HomeKit and not via Matter.