I've been researching this for a couple of days now and looks like it's not possible to keep bluetooth connection alive while the phone goes to sleep or if the app is in the background. However, I have found one app that claims they can run all the time: [RunKeeper app](http://itunes.apple.com/ca/app/runkeeper/id300235330?mt=8) says:

What's New In Version 2.5.1.0

* Support for tracking heartrate in the background with Wahoo heartrate
monitor.

Does anyone know how they manage to send heart rate data to the phone while the app is in the background?

UPDATE:

Got it working by adding an entry in my plist under "Required background modes" for "bluetooth-central".