I’ve got a hub in my house, garage and cabin all separated by at least 30m minimum. All the hubs are connected via the site ethernet network. I want to do things like press a button on the house hub and it turns on the garage outside light via the outlet on the garage hub. Whlist setting up an automation on the house hub I cannot see the garage outlet on the house hub so i can’t do it. I can see all my Samsung multi-room speakers across all hubs so I know it can be done. How do I control devices across hubs? This must be a common ask as you’d need this to set off sirens across a site etc. but I can’t find any useful info. I don’t want some convoluted solution using IFTTT etc. as it defeats the point of Smartthings to a certain extent when other products can be seen across hubs. Trying to keep it simple! What am I missing?
There’s no simple way to do this, but it can be done.
See the how to article in the community – created wiki on automating an out building. It discusses the various alternatives for working with multiple hubs. 
http://thingsthataresmart.wiki/index.php?title=How_to_Automate_an_Outbuilding
Also, the only products which can be seen across the multiple hubs are ones on your LAN. That’s why you can share The speakers or a hue bridge. But you cannot see your mesh protocol devices like zigbee or Z wave from more than one hub. Again how to article has more details. And again, it can be done, but not in a simple way. 
I’m sorry, I’m not feeling well, so I’m going to have to leave follow-up discussion to other people for now.
Thanks for the prompt reply and I hope you’re feeling better soon.
I’ve read through the suggested solutions but I think I’ll only have time for those when I retire! I’ve got dozens of buttons/sensors/outlets/power meters/smoke alarms/cameras across the site so most of the solutions would be very complicated.
I thought of the network/mesh reason but as my Samsung TVs (wired ethernet) aren’t picked up I dismissed that reason but you may be correct.
At the moment I have all the speakers playing a barking dog sound when an alarm is triggered so the solution is all there but just not for the other devices.
Have you looked into ActionTiles?
Also I can’t tell from your initial post, but are all three of these hubs located at the same property?
Yes, my house hub, garage hub and cabin hub. All on the same ST account.
No I was asking if they were at the same location. Like on the same network. If they are, I’m surprised you are not running into issues having multiple hubs on the same network.
Yes they’re on the same network. As each has it’s own IP and ST ID why would there be an issue? I actually have a fourth test hub I attach occasionally and they all work fine. So far 
The ST app lets you add extra hubs as a feature so always assumed this is standard functionality so I can cover multiple location out of an individual hub’s range.
I wonder if Lutron switches would show up across all the hubs using their hub on your system like Hue lights would. That might be your solution for lights. As for automations, on an iPhone I can control any automation on both of my hubs (separate locations, separate accounts) without having to open the app. ActionTiles I still think might be your best solution.
Lots of people run multiple hubs on the same ethernet network, they just define each one as a different “location.” You’ve always been able to do that with SmartThings. ( you can’t have 2 hubs on the same Z wave network, which may be what you were thinking of.)
There was a recent twist that was introduced a couple of months ago because of superLAN connect where now you can’t restrict any of your LAN Devices like a hue bridge to just one smartthings “location” because they keep getting automatically discovered by the other hub. That’s been an issue for some people, for example, who use a separate hub for an Airbnb space in their home. But then it’s a plus for some other people who want to automate an outbuilding. So it just is what it is.
But having two smartthings hubs on the same ethernet doesn’t introduce problems for other protocols, they just have to be two different locations on your account.
Damn it, yes that’s what I was getting it confused with.
Also, one of the main reasons that people go to two separate accounts rather than just two locations is because if you have two separate accounts you can use echo with each of them. Right now, SmartThings doesn’t properly expose multiple locations to some of the third-party integrations, and that includes echo and IFTTT.
Maybe but as I already have the kit (mostly samsung) it really shouldn’t be difficult. I can throw more money at it and complicate what should be an elegant easy solution but life really should be easier on smartthings.
Your set up is closer to an enterprise set up than consumer. It’s also not so much the restrictions of SmartThings as it is in your choice of devices you are using. For example, other products that use hubs, you can see across your entire network. Those that are zwave or zigbee you are limiting yourself in range. You are basically wanting the hubs to act like a wireless access point, but that’s not what they are. Nothing in regards to IOT is perfect and nor do they all work happily together. You have to really think and plan out everything and hope that it works. Lots of trial and error. Again, you are directing blame at Smartthings when I don’t believe I’ve ever seen them advertise their product can do what you are expecting it to do.
I’m just using existing functionality that is built in to smartthings. It all works. The solution is just not mature enough yet to implement a pretty basic requirement. I wouldn’t say controlling a device that is connected to your smartthings account when something happens on the same account is unreasonable, especially when all the building blocks are there.
It’s even more complicated because SmartThings iscertified as a Z wave controller, but it is in fact a multiprotocol system and hasn’t implemented some of the optional advanced controller features that other Z wave only systems like homeseer and vera have.
Adding a second hub as a secondary controller for Z wave should be simple. But SmartThings’ cloud architecture means it just doesn’t work well. Even though it’s part of the third-party specification. In fact, SmartThings support specifically tells you not to do it.
SmartThings strongly discourages adding the Hub to another Z-Wave network. We cannot offer support for disconnected Z-Wave devices or the inability to add devices through the Hub as a result of including the Hub into another Z-Wave network.
I don’t blame anybody who bought SmartThings seeing that it was a certified Z wave controller and assumed they’d be able to add a second hub as a secondary. I was really surprised when I found you couldn’t, although I do understand why.
All this aside (we seem to be going off on a tangent) the hardware works. It’s just the functionality that hasn’t been implemented. Seems the other awkward fudges are a lot of work for basic functionality (it works on a single hub) when I’ve already spent the best part on £1000 of kit!
Anyone from the Smartthings dev team know if this is requirement is being worked on?
Thanks for your help guys.
I don’t have multiple hubs in one location they are each a different location.
That’s what I was getting at earlier you CAN control the multi-room speakers from all hubs and each speaker is paired to multiple hubs! I have 9 of them across 2 locations. So the mechanism to enable this must be present for other devices (you’d have thought). This documentation appears to be at odds with what can be done.
Isn’t there some internet based IFTTT kinda thing that can go from location to location through the internet? At least for if this switch turns on here then turn this on there?
(Not at all elegant but you could put in some cheap ESP32s running ST_Anythings, two per hub location, and physically transfer points back and forth. Like press button 1 at location A would push a output to the device at location B which would be read back in by the second one. They would sit on your ethernet and be a physical hand off between the locations. Again…not a good solution but a solution if you don’t have that many points to do and its all “this turns on then turn that on”)
Yes, this type of solution is detailed in the how to article mentioned above. Which is why I said you can do it, but it’s not simple.
http://thingsthataresmart.wiki/index.php?title=How_to_Automate_an_Outbuilding
But the OP was looking for a simple in-platform solution, like you would get if you linked two Vera hubs or two Wink hubs. But SmartThings just doesn’t support that approach. 