The cube sensors are very nice, although very expensive. They are zigbee, but they will not integrate directly with SmartThings as they use a differen profile. There is an API for the first generation, so you might be able to get cloud to cloud integration that way. If they fit your budget, I think it’s worth a try.
They recently began around the kickstarter funding for their second generation, now called Koto, which is intended to include IFTTT. So that could work nicely with smartthings, assuming you live in a region where IFTTT working. But the planned completion date isn’t until March 2016, and who knows what will happen.
If you read any of my posts on kickstarter projects, you know that I feel that no product can be effectively evaluated until you can buy it for two day delivery from Amazon. Until then everything is just marketing. So who knows what features it will actually be delivered with.
Therefore, I am not suggesting that you be an early funder. But they are a legitimate company with a generation one product which is shipping now, and some very interesting engineering. I would certainly keep an eye on the second generation.
And you can consider whether you want to look into the first-generation now. Their plan is for the second-generation to be backwards compatible, the plans can change. So if you buy it now I don’t think there’s any guarantee that it will work with IFTTT eventually, even if the new generation does. But maybe. That would be really nice.
The other product out there is only for iOS, is HomeKit, and does not integrate in any way with SmartThings that I know of. That’s the Elgato. But it’s something to look at. Nice app, FWIW.
Personally, I’m more impressed with the engineering on the cube sensors. Those folks have done some nice work. But they are very expensive, and I just don’t know what kind of integration you can get.