see - sc.judiciary.gov.ph/jurisprudence/2013/february2013/191023.pdf
"x x x.
In People v. Johnson,16 which also involved seizure of a dangerous drug from a passenger during a routine frisk at the airport, this Court ruled
that such evidence obtained in a warrantless search was acquired
legitimately pursuant to airport security procedures, thus:
Persons may lose the protection of the search and seizure clause by
exposure of their persons or property to the public in a manner reflecting a
lack of subjective expectation of privacy, which expectation society is
prepared to recognize as reasonable. Such recognition is implicit in airport
security procedures. With increased concern over airplane hijacking and
terrorism has come increased security at the nation’s airports. Passengers
attempting to board an aircraft routinely pass through metal detectors;
their carry-on baggage as well as checked luggage are routinely subjected
to x-ray scans. Should these procedures suggest the presence of
suspicious objects, physical searches are conducted to determine what the
objects are. There is little question that such searches are reasonable,
given their minimal intrusiveness, the gravity of the safety interests
involved, and the reduced privacy expectations associated with airline
travel. Indeed, travelers are often notified through airport public address
systems, signs, and notices in their airline tickets that they are subject to
search and, if any prohibited materials or substances are found, such
would be subject to seizure. These announcements place passengers on
notice that ordinary constitutional protections against warrantless searches and seizures do not apply to routine airport procedures.17
x x x."
