A Warning to All

History

No one can say for certain how long there have been large bells in towns and cities around the Empire. On a day to day basis, they are used to mark the passage of time or to call people to prayer. However, when necessary, they are used to call out a warning.
It is believed that this started because of an Onmyouji, many, many years ago, back when the Bureau of Onmyou was in its infancy. The Onmyouji travelled to a remote town to inform them of the imminent arrival of the Night Parade - a carnival of hundreds of spirits and demons that would travel through the town at night and steal away with anyone they came across. Despite setting off in good time, the Onmyouji came across many trials in his path and by the time he arrived in the town the sun was already low in the sky, dusk only minutes away.
The Onmyouji had to act quickly in order to spread the news of the incoming danger. Seeking a means of getting a message to everyone in a short period of time, inspiration struck when the local temple bell rang out the hour. Wasting no time, the Onmyouji hurried to the temple and the hanging bell. He struck the bell four times in quick succession, paused for a moment as the sound reverberated, then struck the bell again. He repeated the pattern - four strikes and a pause, four strikes and a pause - over and over again as the sun slid lower and lower in the sky.
Those nearby came to see what the commotion was about and were told of the coming of the Night Parade. They helped to spread the word until soon enough the entire town was locked away behind closed doors.
The Onmyouji waited until the last possible moment to leave, ringing the bell for as long as possible to ensure that everyone would know and have time to get to safety. Only when he could hear the sound of the Parade aproaching through the streets did he abandon his post and seek refuge in the temple.
The next day, when the Onmyouji returned to the Bureau, he spoke of what he'd done and how everyone had managed to get to safety. He pursuaded his colleagues that this was something that could be implemented across the Empire. There were bells already in most towns and cities, even some smaller villages. All it required was getting the message out so the bell could be rung in time. With plans to increase the Bureau's numbers so that there was an Onmyouji in every settlement, it wasn't long before news began to spread; four quick rings and a pause repeated meant the Night Parade was on its way.

Execution

To warn of the expected arrival of the Night Parade, the bell is struck four times in quick succession, followed by a pause just long enough for the sound to die out.
If a town has advance warning from an Onmyouji that the Night Parade is coming, this pattern will be used four times every hour on the unfortunate day, up to half an hour before dusk. During the last half an hour, the pattern will be repeated without interruption until dusk, to make sure all who hear it are aware that the arrival is imminent.
Traditionally, whilst anyone may perform the ringing earlier in the day, it is the local Onmyouji who will ring the bell in those last thirty minutes. Sometimes, however, they will let a shikigami (a magically powered construct) take their place in order to make sure they get to safety in time.

Components and tools

All that is required for this ritual is a great hanging bell (also known as tsurigane or ōgane) and a mallet or suspended beam with which to strike it.
The bells are usually made of brass, ornately decorated with a reinforced section, where the bell is to be struck.

Participants

With most bells being located in temples, it is usually priests or their students that are in charge of ringing the early warning alarms. The final alarm - the constant sounding in the last half an hour - is traditionally performed by the local Onmyouji, though they will sometimes delegate this role to a shikigami (a construct).

Observance

The warning bells are rung in this manner only when the Night Parade is expected to arrive in that settlement. This is predicted by the Onmyouji, who will then inform the local temple so that the early warning can be issued ahead of the main warning on the approach of sunset.