Turn bluetooth on automatically when connected to Thunderbolt display

I use a MacBook Air as my primary machine.
When at home in my office, I plug it in to a 27″ Thunderbolt display, and use the Apple keyboard and “magic” mouse – which are connected via bluetooth.

To save battery, when not plugged in, I turn off bluetooth.

When I come back to the office, it’s usually still off, and I have to remember to turn it back on, to use the external keyboard and mouse.

I was looking for a way of automatically turning it on when the OS detects it’s connected to an external display, but couldn’t find anything obvious. Until I stumbled across ControlPane

• Create a context of “Plugged In To Display”
• Select ‘Attached USB Device’ in the Evidence Sources tab
• In the Rules tab, click add, then “Add ‘Attached USB Device’ Rule… – then select the ‘Plugged In To Display’ context
• Finally, in the ‘Actions’ tab, click add System Preferences Actions > Toggle Bluetooth. Set it to ‘On’ and ‘On Arrival’

That should be it!

Now, every time I plug my MacBook into the Thunderbolt display, Bluetooth turns on automatically!