The Cooper is one of those devices which can drive you crazy. It can operate locally through direct zwave association even if the smart things hub is missing altogether once the original association is set up.
However…It cannot “run locally” in the SmartThings environment because it requires a custom device type handler.
So you would be in a situation where pressing on the auxiliary switch on the wall would send a direct message to the master switch which was controlling to load to the light fixture and the light would come on even if the Internet was not available. But the switch would be invisible to the official smart lighting feature if the Internet was out because it has a custom device type handler.
I know that’s tedious and confusing and I apologize for that, it’s just the way SmartThings works. It was originally a cloud-based system, and then they stapled a little bit of local processing onto it. But they are philosophically absolutely committed to being a multiprotocol system, which is a good thing, but it means they don’t always expose features (like Association) which are only available with some protocols.
So lots of US members in the community are using the Cooper switches and really like them, and it does mean that the auxiliary still works when SmartThings is being flaky, just as the brands that use physical travel wires still work, but it’s not working through the official smartlighting feature. It’s working through Z wave association, which, to be honest, SmartThings kind of likes to pretend doesn’t exist because you can’t use it to associate a zigbee device to a Z wave device and they want everything to be protocol-neutral.
If you want to use the official smart lighting feature and the local processing that is available through SmartThings, you need a device which can use the generic Z wave switch device type handler. And to be honest I’m not sure if that works with the Cooper battery model or not.
@lgkahn might know, he ended up writing his own device type handler for the Cooper, but I know he’s done a lot with those switches and he might know if they could use the generic handler and operate with the local processing feature of SmartLighting.
But in the SmartThings environment, it’s two different questions. 1) Will the add on switch work if the smartthings hub is running SmartLighting locally and the Internet is not available and two) will the add on switch work if The SmartThings hub itself is not functioning.
There are some devices where the answer to the second question is yes but the answer to the first question is no. I think the Cooper 9540 might be one of those, but as I say I’m not 100% sure.
Note that even if it is one of those, the Cooper battery switch would work with smart lighting just fine if the Internet was up. And you could set things up so that it was using smart lighting with a custom device type handler when the smartthings cloud was available, and relying on Z wave association when The SmartThings cloud was not available. I think quite a few people use it that way.