Bluetooth earphones + nexus 5

Been searching on google and couldn't find an answer.

When i'm using my bluetooth earphones with my nexus 5 the notification sounds come through the earphones (e.g. hangout notification) but they also come out of the phones speaker too.

How do I make it so notification noises only come through the bluetooth earphones? (when they are connected)

Have I overlooked a simple menu option?