When members of parliament are required in the Senate or House of Representatives for a division—a counted vote—the bells ring for 4 minutes. This allows members enough time to get from wherever they are in Parliament House to either the Senate or House of Representatives in time to vote. If a second division is called straight after the first, the bells are rung again for only 1 minute.
Members of parliament (along with all other building occupants) are alerted to a vote being called by the bells and lights that sound and flash in the over 2700 clocks throughout the building. After the bells have finished ringing, the doors to the Senate or House are locked and all members who arrive after the doors are locked cannot vote in the division.
For more information see our fact sheet on Voting in Parliament.