In order to enter the airport, you must show proof of identity and flight documentation (such as an itinerary) to uniformed, armed guards stationed outside the entrance of the airport. After reading a bit, this heightened security must be due to some of the recent bombings in Mumbai. Metal detecters are everywhere in the country, including the entrance to shopping malls and other high profile public places. Ironically, none of the places that employ these devices actually CARE about the result.
That said, they’re an excellent way to access the city. They’re affordable, readily available, and their open-air nature really allows one to take in the spectacles, cacophony, and (sometimes) smells of the city. One of the perils of being a westerner in India (or really anybody that one can identify as not being born and raised locally) is that often others will try to take advantage of you. This certainly isn’t restricted to auto drivers either, as this will also happen on the street, in shopping malls, at the airport, and generally everywhere.