Thanks for your question.
A division is a way of voting in the House of Representatives and the Senate. Members and senators move to one side of the chamber or to the other, to show that they are in favour or against the matter on which they are voting. The members or senators on each side of the chamber are counted and the results are recorded.
The doors are locked so that there is no confusion during the count caused by members or senators entering or leaving the chamber. Those who are in the chamber are counted; those who are locked out are not counted.
If you want more information about voting in the chambers try our fact sheet.