Best answer: As of November 2018, nothing more than tell the temperature of the room it's in. But that means it can be included in routines, and Amazon has developer functionality in place, which should prove to be useful for smart thermostat manufacturers and more in the near future.
Amazon: Amazon Echo Plus (2018) ($150)
If you build it, they will come
The second-generation Echo Plus includes a temperature sensor that can collect the ambient room temperature where your Echo Plus is located. Right now, you can find this sensor listed in the Alexa app and if you build a group that includes it, Alexa will tell you the temperature if you ask. This isn't the most useful thing most of us can imagine, but it's also only the beginning.
Having a reliable way to measure temperatures in a dedicated place means advanced users can build routines based around the readings. A complex series of simple routines that can adjust a Nest Thermostat, for example, based on the temperature readings could be built and the Echo Plus could replicate the features of a remote sensor. For most of us, building 20 or more routines to adjust a thermostat when specific temperatures are reached (remember, if you turn a thing on, you have to tell it when to turn off and vice-versa) isn't very practical, but when you think about something like a smart plug controlling a fan, it gets a lot less complicated: on when it gets above a certain temp, off when it gets below a certain temp.
The exciting part is Amazon's developer documentation and interface for the temperature sensor is already in place. This means that it can be used directly in an Alexa Skill for any device that would benefit from having it. Things become much more useful when the Nest Skill or the Ecobee Skill can use an Echo Plus as a stand-alone room sensor. All the single digit adjustments you need to make to include the temperature sensor in a series of routines can be done away with and you could simply tell your Ecobee 4 to use your Echo Plus as the current room temperature.
We're looking forward to seeing companies leverage this unique hardware feature of the Echo Plus and will be sure to share any news and help get you up and running when it happens.
An Echo with extras
The 2018 Echo plus not only brings Alexa and all her usefulness to a valid stand-alone smart hub. The addition of a temperature sensor means we could see integration with smart thermostats in the near future.
