Hackers at Onion.io have demonstrated using Cortana, the Digital Assistant in Windows Phone 8.1, to control appliances like lights or even print.
The feat relies on a cloud back-end for Internet of Things Appliances and the unique extensibility of Cortana, a feature not available on other platforms.
For simply switching lights on and off I suspect the application is an overkill, but I think with a bit more intelligence we could see a real application in managing an energy efficient home very simply.
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