What is the purpose of padlock when Bluetooth Preferences is opened from the debug menu? When Bluetooth Preferences is opened while holding Shift+Option (bluetooth debug menu) a Padlock appears to the right of the "Turn Bluetooth Off/On" button.

Anyone know what this is for?
That prevents turning off the bluetooth card.

It locks the "Turn Off" button with your password [admin users only]. So the bluetooth card cannot be disabled, unless you click the lock again and input your user password (considering you are an admin user) or any other username/password with admin privileges.