The annex where Anne Frank and her family and the van Daans have moved from Frankfurt, Germany, is in a warehouse in Amsterdam, where people work below the "Secret Annex" in which the families are hidden.  Since these workers are only present during the day, after they leave, Anne and her family and the van Daans, and Mr. Dussel, who joins them later, can move about the rooms freely and not worry about making any sounds.  Also, the warehouse is noisy with machinery running, so if the residents of the "Secret Annex" do make slight noises, they will not be heard.

The door to the "Secret Annex" is hidden by a bookcase; no one has really gone up the stairs since it is assumed there is nothing there.  So, the residents are reasonably safe, but there are some suspicions among workers. On several occasions, the residents hear break-ins downstairs in the warehouse and worry that if someone has heard them, he/she may trade information for immunity from their crime.