But these days I have quite a different reason to feel profoundly irritated with airline security. Last week, my hand luggage mysteriously vanished as it went through those X-ray machines in JFK. And, to my shock, I have subsequently discovered that there is no way of telling what happened, since "improved" CCTV only covers part of the airport.

Hence, I am not only feeling annoyed. I am also wondering afresh about the social and psychological impact of all these cameras. Has all that trillion-dollar security spending actually made us "safer"? Or do such elaborate screening rituals cause us to turn off our brains? And how do we define safety anyway, at a time when political candidates for the 2012 election keep bandying about the word "security"?

My own story was grimly revealing. Last month, late one Friday night, I flew to England on American Airlines, via JFK. Since I was travelling to family celebrations, I had most of my favourite clothes with me in a black wheelie bag, which I took as hand luggage, ironically because I did not want to risk losing my belongings (according to a recent CBS report there are more than 200 reported thefts a day from checked luggage at JFK).

Since it was late at night, the airport was half-empty, so I navigated the ticket line with ease and, half asleep, loaded my black bags on to the X-ray machine. But then, as I went into the body scanners, I looked away. And when I re-emerged, my black wheelie bag had completely disappeared.

Shocked, I hunted around the X-ray machine ausing consternation among the guards and then we all dashed to the only other flight that was departing at the same time, to Qatar, to see if someone had my bag. But nobody on my flight, or the Qatar flight, confessed to taking it, and since the bag was scruffy, with a very wobbly handle, a mix-up seemed unlikely. Thus, when it had still not reappeared after several days, I came to the sad conclusion that somebody had probably stolen it, along with my favourite dresses. Or as Raymond Dilena, the charming police detective on my case, observed: "With the ID you had in the bag, and the tag, I think it should have turned up by now, so I kind of agree with you about it being stolen."

But, I asked, why not just scan all those cameras to see who picked it up? That, it turned out, was impossible: though the CCTV cameras had filmed me as I placed my bag on to the X-ray belt, "There was no camera coverage on the exit side of the machine," Dilena explained. Apparently, the Port Authority, which oversees those CCTV cameras, films the entry, but not the exit to the X-ray machines.

This is bizarre, and thought-provoking for several reasons. Most obviously, it should serve as a warning for other travellers. To be fair, the Transport Security Administration's own website does try to warn passengers about the risks of X-ray machines, noting that passengers should "ALWAYS watch your belongings as they advance through the X-ray equipment at the security checkpoints for secondary screening, INSIST that your belongings be brought to you!" But it is sometimes impossible to do that in body scanners, and many people (like me) get lulled into a false sense of safety, precisely because there are lots of police are around. Little wonder, then, that the TSA says that while thefts from X-ray lines are "not common", they occur, usually because people whip things out of bags, such as wallets. "Just because someone has bought a plane ticket doesn't make them trustworthy," one TSA official explains.

That points to a bigger question: namely whether this surveillance spend is lulling us into a false sense of security in a wider sense. The TSA and other Washington agencies insist that they need to keep spending heavily because the terrorist threat is very real. But some critics in Congress are now questioning whether this surveillance is effective, either in security or cash terms.

In truth, settling this debate either way is tough, since so much data is secret. There is no public information, for example, on whether the bizarre practice of filming only half an X-ray machine is widespread, or whether I was just unlucky. Nor are there any statistics on how many bag disappearances occur at security checkpoints, or whether these are thefts.

As it happens, my own particular story has a happy ending: a week after my bag first vanished it reappeared in the hands of a delightfully friendly American Airline employee in Dallas, seemingly with its contents intact (though I have yet to see the bag to verify it.) But the mystery of why it vanished in the first place will never be resolved without CCTV footage. Either way, the whole experience has been a potent wake-up call. Security is not always as "secure" as we like to hope.