Fitbit has revealed in a post on their forum that the company is working on an app for the Windows Phone 8.1 platform. The app was so far only available on iOS and Android, which meant those on Windows Phone devices couldn’t use the accessory.
Accessory makers have general avoided the Windows Phone platform like the plague, mostly due to the lack of popularity of the platform, which doesn’t make the cost of developing and maintaining the app worthwhile. There have also been technical limitations on the previous versions of Windows Phone that prevented developers from making such apps, which have seemingly been taken care of in the latest 8.1 update, so one could expect more apps in future.
There is no date yet as to when the Windows Phone app will be released.