Two question on Bluetooth development on Android:
Is there a way to enable Bluetooth to be always on (I might have a long device discovery phase in my application) in Android? As far as I can see the default value is a count down from 120s.
Does it exist any open source Bluetooth API implementations?
Enabling Bluetooth to be always on, may not be a good decision, if your only concern is long discovery delay ("battery life"-wise).
As for third-party Bluetooth APIs, the only thing that I've heard of is iAnywhere Blue SDK (from Sybase, not free, only evaluation version available), which covers some of the features, that will be supported in the future from the system/bluetooth and bluez packages.
According to the Android's Bluetooth roadmap, most of the long waited things like Java API, Bluetooth 2.1 + EDR will be implemented, at one point in the future.
Good luck with your project.
The Bluez stack on Linux is an open source implementation. It's also available on Windows but the API is much more complete on Linux.
When you say, 'enable Bluetooth to always be on' do you mean, always trying to discover other devices?
Most bluetooth chips have a deep sleep mode, where the chip is mostly down and just comes up a to check for activity on any established links. It will only wake up to full power when you want it to do something (discovery, make a connection) or there is activity on an existing link.
Yeah, it uses more battery power than if the Bluetooth were totally off but it's not a total vampire.