Kohanim stood guard at three spots in the Temple: in the Avtinas chamber (where the incense was prepared), in the spark chamber and in the fire chamber. The Leviim stood guard in 21 spots: the five gates of the Temple mount, its four corners (i.e., of the Temple mount walls) on the inside, the five gates of the courtyard, its four corners on the outside, one in the lamb chamber, one in the curtain chamber and one behind the Holy of Holies.
The Temple mount supervisor would make a circuit of the watches with burning torches preceding him. If a watch on duty didn’t stand to greet him, the Temple mount supervisor would call out a greeting. If the watchman was found to be asleep, the supervisor would strike him with his staff; he was even permitted to set fire to the offending party’s clothes. The people would ask what the commotion was and they would know that it was a Levi being reprimanded for falling asleep on duty. Rabbi Eliezer recounted that his mother’s brother was once found asleep on duty and they set his garment on fire.