bar (noun) struck in a certain pattern by an iron hammer. When heard, it signifies the divisions of the day in certain houses. May also serve as an alarm (see alarm bar).
At that moment a bar, struck in a certain pattern by an iron hammer somewhere in the house, rang out, the sound taken up by other bars, also struck, on various floors of the House of Cernus. The day, I had discoved, was divided by such signals.
Book 5, Assassin: pg 85