>>it's been suggested that you can super-glue flints for a Zippo lighter to the side (in the groove ) of an old key or a blank,

I made a couple of those up for myself a while back and still have them. They're quite cheap - you can buy the flints for about $1, and most everybody has at least one old key lying around that no longer fits anything.

I used to carry one around on my keychain with no protection, and discovered after a couple of months that there were no longer any flints on it. Kind of defeated the purpose. The original post suggested that you should put some shrink tubing on the key. This is easier if you use a key blank (the sharp teeth on a cut key will probably cut the shrink-wrap and you'll end up losing it, and then eventually the flints will get jarred loose).

If you use an old key, see if you can get the local hardware store to run it through their key cutting machine and shave it flat.

I made my first one up (well, after discovering that they fall apart without protection) using blue shrink tubing. But I subsequently made two more using clear tubing. I have one on each of my key-chains and have taken them through airport security several times. I'll wager not one security guard in a thousand would give it a second glance; even if they looked closely, I doubt they'd notice anything. (It probably helps that the flints are the same colour as the key - silver. I've also seen flints that are a gold colour, in which case a brass key blank would be better.)

On one of my key rings, I carry a SAK Classic; that one always goes in my checked luggage when I travel. The other has a key ring I got as a freebie many years ago, and has a metal plate attached to a leather fob. This plate can be used quite effectively as a striker.

Striking a spark from this device does take a bit of practice, as the flints don't wear evenly. (I have 5 flints glued in a single line on my key.)

One of these days I will borrow a digital camera and take a couple of pictures of my key rings for anyone who's interested.

The shrink tubing came from Radio Shack - they sell a bag of assorted colours and diameters. (If you're a Ham operator, you should have a couple of bags of these, just for your image; if you're not a Ham, shame on you <img src="images/graemlins/grin.gif" alt="" /> )

In general, I don't think there's a foolproof rule about what will or won't get confiscated. I once had a Coghlan's wire saw confiscated; the security guard had to ask me what it was, but as soon as he heard the word "saw" he decided it was an unacceptable item. <img src="images/graemlins/frown.gif" alt="" />