I will be traveling at Christmas with some gifts including 2 rolex watches and their boxes, 2 or possibly 3 iPads and other electronics including my dslr and several expensive lenses. I seem to lose sight of my carry on luggage for some time as it goes thru screening, especially should I be selected to get additional screening. It would take just a moment for someone to lift a valuable or two out of my bag.

I have never noticed it done, or addressed here or elsewhere, so can someone tell me: are you allowed to lock your carry ons as they go thru screening?