The bell was actually installed the day before he [King Valdemar] died, but the rope to ring it hadn't been hung, and it didn't have a clapper. So you can imagine that when a strange bell was heard tolling before dawn the next morning, people were pretty startled. When they went out to look, they saw what you'd see now if you were to go out to the Field— every Companion here gathered around the tower and staring at it. When they got back to the Palace they learned what the Heralds had already known— that Valdemar was dead."
In present-day Valdemar, the temple is long gone, but the bell tower remains. The Death Bell rings every time a Herald dies.
It may also ring when a Heraldic trainee dies.
The Death Bell rang when Tylendel died, shortly after he was repudiated by his Companion, Gala. This was widely perceived as a sign that Tylendel was forgiven for his actions, and was the reason he was buried in Heraldic Whites, with the honors of a full Herald.