It’s a very good question, and the answer at this point is that if you use smartthings you are able to create much more complex rules than you can with the other systems you described. And you can also add Zigbee and Z wave devices if you were interested in that.
But if the combination that you have does everything you want it to, there’s no reason to add a smartthings hub.
See the following FAQ for more details. (The topic title is a clickable link)
SmartThings can use the hub, but SmartThings is not the hub. I say this because the hub is primarily the tool used to allow SmartThings to control Zigbee and ZWave devices in your home. If you dont have any of those but still want to use the automations etc. , you can absolutely use SmartThings without a hub. The scenario you describe integration between cloud services such as Google, and Harmony could be setup with SmartThings even if you dont have a hub.
Now, If you want to add a ZWave or Zigbee smart switch, or bulb etc… Then the hub becomes required.
No local integration for the Harmony hub, but if you used the KuKu Harmony, it would connect tonthe Harmony hub using REST calls to the Harmony hub in developer mode. That said its a very advanced and complex setup and not typically something I see as a first attwmpt at integration.
Most. There are exceptions to every rule of course… But generally speaking yes, any industry standard Zigbee or ZWave device. Some devices may require custom code to make them work properly but you’re heading down the right idea.
Zigbee has multiple profiles and only some of them will work with smartthings. Short answer is those using the zigbee home automation profile (ZHA 1.2), or the newer Zigbee 3.0 profile. (But not devices which require “touch link commissioning“ or “Zigbee green power” neither of which are supported by the smartthings hub.)
See the profiles FAQ (the topic title is a clickable link)
Hue devices are Zigbee 3.0, but should still be used with the hue bridge.
If a zwave or zigbee device does work with smartthings, then you will not usually use its own hub/gateway. (Again, Hue is an exception because technically it’s a bridge, not a hub. It forms its own mini Zigbee network and then communicates with other platforms, like smartthings, by LAN or cloud to cloud.) so for example if you get IKEA Tradfri Zigbee Devices, you would connect them directly to a smartthings hub rather than using the IKEA Gateway. The same with Xioami zigbee devices.
Let’s see, what else.
Z wave “local scene” controllers will not work well with smartthings. There aren’t too many of these around anymore, it’s an older technology. Z wave “central scene“ controllers will probably work with smartthings, but may need custom code.
Most Z wave devices will work at the “basic“ level for on/off/Dim, but may require custom code for more advanced features which are an optional part of the specification.
One more thing: smartthings has never been very good at “multi endpoint“ Devices, whether they are Z wave or zigbee. So if you are looking at multi button devices, always check the forums first to make sure that particular device works unless the manufacturer has specified that the device works with smartthings.
To be honest, it pretty much all comes down to the first rule of home automation: “the model number matters.“
While the smartthings hub has both a zwave radio and a zigbee radio, that doesn’t mean it will work out of the box with every Z wave device or every zigbee device, or that it will have access to all the features of those devices.
But if I purchased a compatible motion sensor, would I be able to program smartthings to activate google home and give a verbal weather report when I walk by the sensor on only work days marked on my google calendar during specific times (when I wake up normally to get ready)?
I will defer to someone else on googles capability to trigger a weather report based on seeing a motion sensor (you would use a Google routine for that, unsure im an Amazon person) but the ability to report a motiom event from st to Google is easy.
Amazon echo is much more advanced in the features that its routines offer than Google is, so far. I expect google will catch up eventually, but they are definitely not there yet.
So it’s relatively easy to set things up so that you can make echo devices themselves do quite a few different things. Including speak a weather report, make a custom announcement, Ring a chime or play a barking dog audio, a whole bunch of other things. This is done through “Alexa routines,“ (not smartthings routines).
Google so far has not opened up the Google assistant devices to similar third-party controls.
Google assistant routines can do most of the same things as the “action“ In an “If This, then that“ format. The problem comes with the “if,” or “trigger.” So far, you can only trigger google assistant routines by speaking a custom phrase or from a scheduled time of day.
In contrast, Alexa
What is a trigger? A trigger is the event which makes the Routine start. It can be a voice command, an alarm, a scheduled time, smart home device interaction, geolocation, or Alexa Guard. This is the event Alexa needs to detect to know to start your Routine.
. What is an action? An action is the thing you want Alexa to do. It can be almost anything you can do with Alexa using your voice like asking for the weather, playing the news, controlling compatible smart home devices, reading out your calendar, checking your emails, making a call - you’re only limited by our imagination.
. What is a custom action? Custom actions let you type in anything you can normally say to Alexa as an action in a Routine. Custom actions need to be the last action in your Routine. Learn more about Custom Actions.
So it’s easy to set up an Alexa routine which is triggered by a motion sensor. But right now there is no official way to do that with a Google assistant routine.
There are some workarounds you can try, but they still don’t offer as many features and they require all of that additional setup you wanted to avoid.
Again, though, it does seem likely that Google will add more kinds of triggers eventually.
The problem you’re running into is there is no single service that has all of the capability. And because no one automation fits the needs of all users, the services that do have the capability don’t even TRY to solve it for you - they just provide the user the tools to build the automations they want. (People don’t realize no matter how cool Home Automation is - it’s still in its infancy. You will find more you CAN’T do without jumping hoops than things you can do natively - that goes for all platforms.)
The part that causes custom code is that part that says, OK, I just got a motion alert. Should I let Alexa / Google know? Let me look at this calendar and find out. ok yeah I should -trigger alert-
Google has the calendar - great. Voice response yeah - but voice response based on calendar doesnt exist and it can’t (generally) connect the devices natively unless they’re wifi direct connect devices. if they could do the devices, they still don’t have the advanced logic capacity so you’re stuck there.
SmartThings could be the interconnect for the device, and has the logic capability - with custom code but does not have a voice engine
Alexa or Google could be the voice interface, we’ve already covered Google - but Alexa like Google doesn’t have advanced logic in its routines. I can trigger weather based on a sensor I can even limit it for time as JD said - but no conditional logic. you need something else for that.
You need a platform for the ‘brains’ something that can provide an advanced rules / logic engine. (Which your ask is not trivial, btw)
Google / Alexa simply don’t have the logic capability right now to make those conditional choices. They are simply voice input, and voice output based on simple triggers. and very basic conditions. So no matter which way you look at this, or what platform you choose to drive the logic portion of this, be it SmartThings, Home Assistant, Hubitat or anything - you’re writing some kind of automation to make that determination.
Additional unsolicited advice:
People love to play around with triggered voice. It gets REALLY old very quick. The novelty will wear off in a couple weeks, then it turns into annoyance. When I was new at it, I literally spent DAYS going through various things to make Alexa ‘speak’ when various items happened in my home. It lasted a month and I was told by my spouse in no uncertain terms it all needed to come out… I didn’t mind because by then I was tired of doors and windows and things causing Alexa to say stuff… The only announcements that remain in my system are an announcement if someone’s on my front porch at night or if the garage doors are open after dark. So if you were to ask me how I would do it - my VERY FIRST question is why are we doing this and is it really necessary?
So, lets assume it is - the easiest way for me to do it right now: (Don’t worry about the how - these are just the big blocks)
SmartThings Virtual Switch - let’s call it weather announce.
Alexa Routine to speak weather to my chosen device when the virtual switch is ‘on’
My favorite motion sensor in SmartThings
The GCalSearch SmartApp configured to read your google calendar for an appointment named (insert name here)
SmartTHings Automation to turn on the weather announce virtual switch if motion is detected and the GCal Search virtual device created in step 5 are both on at the same time.
SmartThings Automation to turn off the weather announce virtual switch after it is turned on.