Utili-key "knife" and airport inspection?

In practice (as opposed to "officially")...

I carry one of these on my keychain, with 6 or 7 other keys. I've flown US domestic flights with it about half a dozen times and never had a problem.

I gave one to all my coworkers for Christmas a few years back. One of these coworkers is a Muslim woman who wears a hijab. She flies a lot, and ALWAYS gets selected for "random" extended screening. At least once, she accidentally left the Keytool on her keychain and got through security with it.

Anecdotal, surely, but I think telling. The thing is just not very noticeable.

Most airports in "Schengen" follow all of

1. the EU guidelines
2. the IATA guidelines
3. their own rules which they change every week (or while you are being controlled, or which the security guy makes up any way he feels)

... whichever is the most restrictive. The Frankfurt airport makes the first two available online in concise form, although only in German: [1] [2]

[1] is taken from EU185-2010, which contains another 50 or so pages of rules, such as you have to legitimate yourself with a boarding card and passport, or how your hand luggage must be searched, and what amounts of liquids and aerosols you may take with you (there's also EU 300-2008, but that one is pretty irrelevant from the PoV of a traveller).
Regarding your tool key, it mentions "sharp or pointed items such as [...] razor blades, cutters, [...] knives or sciccors over 6cm, martial arts instruments with a point or edge". Of course razor blades are more like 3cm, not 6cm, so it's a bit moot. It also mentions "tools which might cause severe injuries or be a hazard to aviation", giving drills, saws, and blades as example (among others).

[2] Does not seem to contain anything about weapons or weapon-like items other than tasers and ammunition. Funnily, it disallows tasers and other "incapacitating items" (quite obviously) but explicitly allows carrying a defibrillator. It also forbids lithium batteries over 100Wh, but that's usually not a problem since your laptop will have only about half as much.

Your tool might easily be seen as 6cm knife, or "sharp" or "pointed" item in general, or as a kind of kubotan (= pointed martial arts instrument). It might also qualify as "saw" or "tool blade". Insofar I wouldn't risk taking it with you, security personnel isn't well-paid, and they might want a tool key for free.

You probably do not need to fear prosecution, though. EU 185/2010 very clearly states that if something is detected, you are either denied passage to the "fly side", or the item will be confiscated and you must undergo a new examination until the examiner is satisfied. I'm not a lawyer, but from this very explicit wording (and the absence of mentioning penalties) I'd guess it is quite clear.

I've had my UtiliKey for over 10 years. I keep in my carry-on bag with my keys. It has been all over Asia, parts of Africa and the USA. Today, Narita Security found it and declared it illegal. Confiscated! After ten years!

In the US, certain "tools" are not allowed on planes any more than "knives". I had left a small Torx wrench in my pocket once - like an Allen key but with a star shaped head, about 8 cm long. It was confiscated as a "tool" (I guess they thought I would unscrew the cockpit door with it). But that was about 10 years ago.

These days, the TSA prohibits any tools over 7 inches (17.5 cm) length in carry-on, as well as any sharp objects, with the the following exceptions:

In general, you are prohibited from traveling with sharp objects in your carry-on baggage; please pack these items in your checked baggage. Scissors with blades smaller than 4 inches, small needles carried for special medical needs, and other sharp objects that do not contain a blade may be placed in carry-on baggage. Any sharp objects placed in carry-on or checked baggage should be properly sheathed or securely wrapped to prevent injury to TSOs and baggage handlers.

Even if an item is generally permitted, it may be subject to additional screening or not allowed through the checkpoint if it triggers an alarm during the screening process, appears to have been tampered with, or poses other security concerns. The final decision rests with TSA on whether to allow any items on the plane.

Handy link: TSA's can-I-bring page

In March 2015, I accidentally left it on my keychain while going through security in a U.S. Airport. The TSA agent noticed my keychain in the bin and asked about the Swiss tech key chain tool. After he examined it he declared it a blade and tossed it in the bin, never to been seen by me again. My advice, leave it home.

I'm a airline pilot and I carry it with me all the time, just recently security took mine. Guess you can't trust us with your lives either...