This technique creates a spherical detection barrier with the user at the centre. At the user's command, the detection barrier can expand, grasping everything in the room. The user is able to detect anything that moves inside the barrier space with their own "sense". The user may also move, the barrier will follow them as they move.
Hō (法) means law, method, or ritual. Jin (陣) means formation or encampment. Hōjin (法陣) is the word used for, for instance, the circle diagrams used in alchemy.