The "One Bar Prison" is the state of being physically free but digitally shackled. You can walk to the park, but your mind is still scrolling. You can sit across from your family at dinner, but your attention is elsewhere. You have the key to the door (the power to put the phone down), but the lock is psychological.
While it could mean one of those, I am answering for the most likely one, which is the , as there are many technical guides and listings for its use. Quick Guide to One Bar Prison Restraints One Bar Prison