Hong Kong Airport Security Unit conducts a drill in front of an audience on the open day celebrating the unit's 40th anniversary, on Saturday, September 9, 2017.Photo: China News Service

To mark 40 years since it was set up, the Hong Kong Airport Security Unit (ASU) holds an open day on Saturday, September 9, to show local residents how they keep passengers and staff safe. Photo: China News Service

An ASU police officer poses with a young visitor and a special police vehicle on the open day held to celebrate its 40th anniversary, on Saturday, September 9, 2017.Photo: China News Service

Weapons used by ASU police officers are on display during an open day to celebrate the 40th anniversary of the founding of the unit, on Saturday, September 9, 2017.Photo: China News Service