I flew CDG-LHR resently and ICTS was checking boarding passes and passports at the entrance to the departure lounge ICTS put a sticker on the BP to indicate that they have checked the passport and the airline checked the passport again a few feet away righ in view of the ICTS people. ICTS asked a asian couple alot of question and thuroughly checked thier passports. The flight was not boarding yet. After ICTS was finished, the couple saw the gate door closed and thaught they were late for the plane, so they walked tro the door and opened it causing a alarm to go off that sounds like an old fashioned fire engine siren that winds up and stays at the same pitch.