What feature is part of the PSU for controlling passenger comfort?

The fasten seat belt sign is an important feature of the Passenger Service Unit (PSU) that contributes to passenger comfort and safety during a flight. This sign serves as a clear visual cue to passengers, indicating when they are required to secure their seat belts, especially during periods of turbulence or other situations when it is necessary for passengers to remain seated. By effectively communicating this safety requirement, the fasten seat belt sign helps to ensure a secure travel experience, enhancing overall passenger comfort.

While the other options mention various features that may be present in an aircraft, they do not specifically focus on passenger safety and comfort as effectively as the fasten seat belt sign. The catering service button pertains more to meal service rather than comfort-related issues, the personal entertainment system offers entertainment but does not contribute directly to safety or comfort regulation, and the temperature control switch affects the cabin environment but is not a direct indicator for passenger behavior in relation to safety measures.