There are over 2700 clocks in Parliament House, fitted with two flashing lights which call members of parliament to the chambers. One light flashes green for the House of Representatives and the other flashes red for the Senate. When the lights are activated, the sound of a bell rings through loudspeakers in the building. Each clock is controlled and sychronised by a master clock. The master clock also operates the red and green lights.
The bells ring for five minutes at the start of each session, or meeting, of the Senate or House of Representatives, and for four minutes if there is a division, or counted vote. Four minutes gives members of parliament enough time to get to either chamber from anywhere in Parliament House before the vote is held.