I am considering buying luggage for my college age daughter that has lockable zips for all outside pockets...with the exception of the zip enclosing the luggage pull. Is that space big enough to hide things? I noticed that you could slip your hand, albeit tightly, all along the backspace of the suitcase. BTW: I was considering the Hovercraft duffel 30 by Eagle Creek.
luggage security is a thorny issue. The bags need to be accesible by airport security so unless she's using a TSA approved lock (which they can open with a master key) it will be cut off if there's any inspection required.
My tip, use cable ties (I think they're called zip ties in the USA) preferably in an unusual colour or a combination of colours. They're easily snipped off by security personell if needed. But, if a drug dealer snips one off to stash drugs it's unlikely he/she will have one (or the time to replace it) or the unusual coloured zip tie.
When you go to the baggage collection to get your luggage if you notice a missing or mis-matching zip tie DO NOT TOUCH the bag, call a security person over and tell them you suspect the bag has been tampered with. It means a little inconvenience as they do a full search of the bag, but at least you (or your daughter) won't be a suspect.
Phil about 8 years ago