Prevent auto-pairing for headphone (Bluetooth) I use my headphones to connect to my smartphone a lot, but only rarely to connect to my macbook (Mojave). 
Is there a way to prevent auto-pairing every time I power-up my bluetooth headphones?
I've tried a option reported for earlier OSX versions

sudo defaults write /Library/Preferences/com.apple.Bluetooth.plist DontPageAudioDevices 1


but that doesn't solve the issue. 
I'd very much like to stop manually disconnecting my headphones every time.
This can indeed be a pain. I myself own and use BT headphones and I rarely connect them to my MacBook Pro laptop. Fortunately, my headphones remember the device I last connected them to, and will auto-reconnect to that device when they power up, but only if that device is available. 

However, this auto-reconnect will only happen if the device (iPad, iPhone, etc) has already been paired with the headphones. So, one way to keep your headphones from pairing with your laptop is to remove the pairing record for it. This is done via the "Bluetooth" preferences panel. Just select the pairing entry for your headphones and remove it by clicking on the "X" button after selecting the right entry.



The only downside to this is that you need to re-pair your headphones each time you want to use them with your laptop.