From TheVerge:

But walking around outdoors proved that the Bluetooth connection is still frail. I had trouble streaming music with my phone in any of my back jeans pockets. ... This would also help explain why the main Facebook group for Dash users is full of conflicting reports regarding these Bluetooth woes — a lot depends on the environment you’re using them in, and how you use them.

“Say you’re taking a train through Newark, there’s a magnetic transformer station that you pass on that train and you could experience a [Bluetooth connection] drop out there." - Bragi CEO Nikolaj Hviid