After the arrival of iOS 8, the Bluetooth has been one of the most common problems of the latest mobile operating system from Apple and iOS 8.1.2 seems that these problems have not finished vanish altogether.
Although there are users who have been able to connect without any problem through bluetooth speakers and other accessories, it seems that there are still others who do not end up having good experiences with this. If this is your case, some users with iOS 8.1.2 have recommended that after "Reset All Settings" bluetooth device has begun to run correctly. To this we must:
Open Settings> General> Reset> Reset settings.
After restarting the Bluetooth device should start working on iPhone with iOS 8.1.2 and although not 100% sure at least worth a try.