As always, The first rule of home automation applies: “the model number matters.” This FAQ is just going to lay down some general concepts about Z wave secondary hubs. It does not apply to Zigbee. It does not apply to Wi-Fi mesh sub hubs. And it doesn’t even apply to all zwave hubs except at the most basic level. But it should help explain the basic concepts. And I’m going to try to keep this as simple as possible at the conceptual level, so there may be a few places where it’s not 100% technically accurate, but it will give you the idea of the impact on your usage of the system.
THE PRIMARY ZWAVE HUB
Every Z wave network is “established“ by a primary controller. Usually the hub. The primary hub is responsible for giving out network addresses, keeping track of the security keys, and adding or removing devices from the network.
A smartthings hub expects to be the primary zwave hub on its network unless it is one of the Wi-Fi mesh subhubs, in which case it will take a subordinate role.
It is technically possible to add a smartthings hub to another network owned by a different brand of primary zwave hub, but it may not work very well if you do.
When the SmartThings Hub is added into another Z-Wave network, it may not receive notifications from some battery-operated devices. SmartThings Technical Support does not provide assistance to consumers using the Hub with other Z-Wave controllers.
It also lacks some of the Z wave utilities that other Z wave controllers may have.
So one of the most frequent questions about secondaries that gets posted to the forum is “can I add my smartthings hub as a secondary to my existing zwave network“? and the short answer is that yes, you can do it, but you probably won’t get the results that you expect.
THE ROLE OF A ZWAVE SECONDARY CONTROLLER
Back when zwave was first developed, everything ran locally, and the theoretical role of a secondary controller was to speed up local communications for a specific set of devices which were physically close together. Like on another floor of the house. Or a handheld remote in a room with several Z wave devices.
When a secondary controller is added to an existing zwave network it should not have any devices already connected to it. You basically have to start from scratch. At the moment that it joins, the primary controller will pass over to it a list of the Z wave devices currently attached to the network. That’s pretty much all that it gets. In some networks you will have the option to allow the secondary to add new devices to the network, but in others not.
Once the secondary is on the network, it can then communicate with the devices in the list it was given when it joined, except that it may not be able to communicate with locks because it doesn’t have the security keys for those.
As mentioned in the note from smartthings support above, most secondaries Will also not receive lifeline messages from some individual battery-operated devices.
If the secondary is allowed to add devices and it does, usually the primary will also know about those devices.
However, it is really common that if the primary adds additional devices after the secondary was added to the network, the secondary will not know that those exist.
There are a few secondaries, such as the Aeotec Z stick, which will continue to query for new device adds and so generally stay in sync with the primary. And vera has its own system for keeping multiple Vera brand hubs all in sync with each other.
but other than that you should pretty much assume that your secondary hub will only be aware of zwave devices that were on the network at the time that it was added to the network. that means if you want to secondary to be aware of devices added after the time that it was it self added to the network, you have to exclude it and re-include it. That can be a lot of work if you have to also rebuild automations.
Nonzwave devices on a multi platform hub
If you have a multi platform hub, like smartthings, and it is on a Z wave network, whether it is the primary or the secondary, you also need to understand the information about any of the other protocols, like your Zigbee or Wi-Fi devices, is not shared. joining a Z wave network just means joining the Z wave network. It doesn’t mean you can then fold in other devices controlled by either hub.
Some platforms, including smartthings and most security systems, assume that their hub will always be the primary zwave controller and results may be unsatisfying if you try to set them up as a secondary, even though technically it may be possible.
If you do want to set smartthings up as a secondary, it should not have any Z wave devices connected to it at the time it joins the other network. It will only know about devices that were on the other network at the time that the smartthings hub joined that network. It will not be able to message locks. It may also have difficulty with some battery operated devices that are trying to use the lifeline group. SmartThings support will not help you if you run into problems when you have a smartthings hub set up as a secondary to a different brand’s primary hub.
If you want to use smartthings as the primary and another brand as the secondary, that may work fine with the same caveats: it may only know about Z wave devices that were on the network at the time that it joined the network; it probably will not be able to message locks; it will not receive lifeline messages. and it will not have any information about the non-Z wave devices on your SmartThings account.
In the past, some people have successfully used one of the swimming pool management Z wave controllers as a secondary, but these are pretty much self contained systems. Quite a few people have added a Z wave USB stick in order to get its mapping capabilities. Also quite a few people have been able to add handheld zwave remotes of various types to act as secondaries for a few specific devices. And a few people have added a vera, for whatever reason, and managed to get what they wanted out of it.
Most attempts to connect to a security system in either direction have not been successful.
So while it can sometimes be done for some specific situations my first question would be why are you trying to do it?
if it’s for a specialty sub system like the swimming pool management systems, that makes sense.
If it’s to tie in your smartthings home automation to a security system, that probably won’t work the way you were hoping.
if it’s for a handheld remote designed for that purpose, go for it.
for any other use case you will probably want to consider alternative approaches.