flatiron in carryon in spain

I assume you mean the normal electric ones? If so it is fine. Same as a tablet or computer or clock or any other small electric item.

Make sure it's dual voltage so you can use it there.

Thanks. My wife wants to buy a good one from there so she can use whenever we go to EU area. We are going to the trouble of making sure to get luggage that fits Vueling carryon requirements and I would hate to go through all that only to find that we have to check the bag anyway because of the flat iron.

EU security rules: https://ec.europa.eu/transport/modes/air/security/info_travellers_en

When packing, you should bear in mind that certain articles, that
may appear harmless, are not allowed in your hand luggage for security
reasons. Such articles would include: gases and sprays such as
pepper sprays; sharp objects such as knives or razor blades; drills or
saws; baseball bats or clubs. Such items will either have to be
surrender at the security checkpoint or will have to be packed into
your hold luggage.

List of prohibited articles in your hand luggage: https://ec.europa.eu/transport/sites/transport/files/modes/air/security/doc/info_travellers_hand_luggage.pdf

e. blunt instruments (objects capable of being used to cause serious
injury when used to hit),

Whether your flat iron is a "blunt instrument" or not would be up to the judgement of the security agent.

I travel to Europe with my flat iron and it's never been an issue. I've had it both in my carry-on and checked bag. You'll be fine.

a flatiron (for hair) not a flat iron (for clothes)

Probably time to rename it an 'uncurling iron' to avoid confusion :-)

aka "hair straightener".

'round these here parts, its more common to hear them referred to as hair straighteners. Flat iron confused me first time I heard it. Noting, that checking my wife's and others in US stores, I haven't seen any that were dual voltage on store shelves.

Noting, that checking my wife's and others in US stores, I haven't seen any that were dual voltage on store shelves.

I bought a dual-voltage one at Target, so I don't think they're too hard to find. I've used it on many trips with just a plug adapter with no issues at all.

When your wife constantly uses one term, flatiron, it becomes conditioned to refer to it that way. Yes, I should have written as "also called a hair straightener". She plans to buy one in Barcelona that will be used exclusively for trips to Europe. My only concern was whether we'd have to end up checking the bag since I am going to the trouble of finding the European sized hand luggage (whcih I did find - I will post a comment on it after I try them out and check dimensions).

My wife always brings a curling iron and has never had any problem. See no reason a straightener should be a problem.

As others stated, she will absolutely need a dual voltage flat iron. I fried mine in England last year (I was defiant - "it won't happen to me", lol).
Sometimes they can be hard to find in a store. Tell your wife to be wary of the ones on Amazon...lots of fakes out there. My hair stylist got me a great one at his cost from his vendor, so it was inexpensive. 👍🏻

She would be getting one in Spain, so should be no voltage issues throughout Europe. She fried one when we went to Italy. So, she thought better to buy one there and use when overseas.