Text alerts while connected to Blutooth

I have an iPhone 7 running iOS 11.1 connected to a neckband style blutooth headset. I prefer to leave the earbuds dangling unless I am on a call or using an app that involves audio. This works well for phone calls because the ringtone is sent to both the headset and the iPhone speakers. My problem is that I only get audio text notifications via the headset, so I only hear them if I happen to have the earbuds in. I have to leave the phone on the desk in front of me so that the visual text notification catches my eye. How can I set it so that I hear the text notifications on both the speakers and the headset?