Microsoft yesterday released Windows 10 Mobile build 10536 to Fast Ring Windows Insider program users. This build is supported in most of the Lumia devices, but there are several other Windows Phone devices which are not supported with Windows 10 Mobile builds. There is a bug which now allows several non-supported devices to install this latest build from Microsoft and Microsoft has now warned users to not install it. If you have installed it already, you might need to reflash Windows Phone 8 OS on your device.
— Gabriel Aul (@GabeAul) September 15, 2015
Windows Mobile Insider Preview currently works with the following phones—as long as they have at least 8 GB of storage, Windows Phone 8.1 was already installed on the phone at the time of purchase, and the version number is 8.10.14219.341 or earlier: