As long as someone has the Joule app, they can connect to and control Joule with Bluetooth. If they want to use WiFi as well, you will have to disconnect from Joule first.
1. Verify that Joule is plugged in and that you are in Bluetooth range, then open the Joule app and navigate to "Settings" > "My Joules" > [Joule Name] and select Disconnect Joule.
Watch the video below to see how it's done.