You can’t spell “harmonica” without “harm.” And you know what they say: First do no harm.

Well, maybe they should say, “Do no harmonica.”

This is all a convoluted way of getting to today’s column, which is about what I call “magnetometer moments.” That’s when an innocent item packed in your carry-on bag raises alarm bells in the airport security line.

Phil Lindberg’s magnetometer moment involved the aforementioned mouth organ. He was learning to play the harmonica and realized the best way to get better is to always have one about your person.

“The harmonica was in my carry-on backpack as I went through security on my way to a work-related conference,” wrote Phil, of Columbia, Md. “Yes, I experienced that embarrassing moment as I was pulled out of the security line to open up my bag.”

The TSA officer told Phil that, when X-rayed, a harmonica can look just like a handgun magazine.

“After considering it — a metal, rectangular object about the right size and shape; the brass harmonica reeds could appear to be a magazine spring — I agreed with him,” Phil wrote.

For the record, Phil was packing a Hohner Special 20 harmonica, in the key of C.

Wrote Phil: “There are those who might consider such a harmonica a dangerous weapon, but perhaps not in the way the TSA is worried about.”

Reid Fisher of San Martin, Calif., usually travels with a capo. No, not a high-ranking member of the Sicilian mafia, but a metal device that is clamped onto a guitar neck to change the instrument’s key.

“Since guitarists often forget their capos, I often carry one to music jobs, and one lives in my dopp kit with the toothbrush, etc.,” Reid wrote. “The model I have is pretty much all steel, with some rubber on it and a couple of pivoting parts.”

It looks a bit weird, like a torture device. That’s probably why Reid was pulled aside while going through security and asked to empty that bag.

“They were very serious until I could credibly explain what it was and how it was used,” Reid wrote. “They were a bit skeptical at first since I didn’t have any instrument, but there were guitar picks and other music stuff.”

Suitably convinced, they let Reid through.

Gaithersburg, Md.’s Ken Glasser is also a guitarist. Sometimes when he travels, he takes his Little Martin acoustic guitar, set up for lap-style playing. And Ken brings a blue pouch filled with guitar accessories: thumb picks, fingerpicks, a tuner, a battery for the tuner and a few capos. Even when Ken doesn’t have his guitar, he has his blue pouch.

After all, wrote Ken, “You just never know when you might run into a Guitar Emergency and I want to be prepared.”

When the pouch is nestled inside another carry-on bag, it often piques the interest of airport screeners.

“Finally, one day a TSA agent said to me it would be easier for everybody if I just pulled the pouch out and put it on the scanner belt alone. Which I’ve done ever since,” Ken wrote. “I really don’t mind. Nobody wants to be the one who let somebody through.”

Linda Ward of Leesburg, Va., writes: “Due to my own personal peculiarities, I travel with a ukulele and an electronic tuner and with my clothes on wire hangers (so that I don’t have to use the hangers in a hotel). I also use facial wipes.”

Apparently, the combination of those three things — the plastique-like density of the facial wipes, the metal wires, the mechanism of the tuner — looks suspicious. Suspicious enough for Linda to get extra attention at the airport.

“I’m a 73-year-old retired first-grade teacher, so it’s very embarrassing to be pulled over for a thorough luggage check-in and pat-down by a whole team of agents,” she wrote.

A ukulele may not be threatening, but the same can’t be said of what Irv Smietan of Fairfax, Va., carried through Heathrow Airport in London about 25 years ago.

As Irv’s bag went through the X-ray machine, the operator stopped it. He spoke briefly with Irv to confirm his suspicions and then called over some of the more junior screeners.

This was a teachable moment. What they were seeing on the screen, the security official explained, was not a pipe bomb. It was a child-size set of bagpipes.

Wrote Irv: “A short time for education and we were on our way.”

Tomorrow: More magnetometer moments.

Twitter: @johnkelly

For previous columns, visit washingtonpost.com/john-kelly.