Passenger service unit
A passenger service unit is an aircraft component situated above each row in the overhead panel above the passenger seats in the cabin of airliners. Among other things, a PSU contains reading lights, loudspeakers for announcements, illuminated signs, buttons to call for assistance, air condition vents, and automatically deployed oxygen masks in case of cabin depressurisation. These are not found on the smallest of feederliners, or on older aircraft.