Since each family clan held exclusive authority for the Temple itself on its day of service, these elders also kept the keys to the Temple court gates with them, in this chamber.
"Within the Place of the Fire, there was an opening in the floor that measured one square amah (about a half-meter square). This opening was covered over by a marble slab which could be removed. A metal ring was fixed into the slab, and it could be removed by pulling on the ring. On the inside of this marble tablet, a chain was attached. This chain held the keys to the gates of the court."
"When the time came to lock the gates of the court (at the close of the day), the priest who guarded the chamber raised up the marble slab, took out the keys, and locked the gates of the court from the inside - from where he stood at his watch, within the Place of the Fire. Outside, a levite stood guard, for at the Place of the Fire, the priests watched from within and the levites from without. After he finished locking the gates, he returns the keys to their place, covers up the stone with his cloak, and sleeps on top of the spot" (based on Midot 1:9).