Can we get a patent for the design of our IoT device?

If your invention involves operation or utility, you should proceed with a non-provisional utility application. If there is also a unique design, shape, contour, configuration, or other aesthetic appearance to your device, you can also obtain a design patent - design patents and utility patents are not necessarily mutually exclusive. And the design has nothing to do with the underlying technology - the design goes strictly toward the appearance of the device - usually, if you refer to any issued design patents, you will have seven views - front elevation, rear elevation, left side elevation, right side elevation, top plan view, bottom plan view, and perspective view. And by the way, currently design patents are protected for 15 years - the law was recently changed from 14 years, effective December 18, 2013.

Design patents protect the ornamental (non-functional only) aspect of your invention and do not depend on whether a utility patent will be granted as well.
However, does the design of your item has an affect on its functionality? If so, you should go for an application for a utility patent.
In general, for a design patent you will need to write an application, according to the USPTO guidelines (basically thoroughly describing your design) and if your design is novel, you will be granted a patent which will be in force for 14 years.