CHARLOTTE, N.C. -- At first glance, it looks like a harmless cat keychain.

But as it turns out, "Cat Eyes" can be used as a deadly self-defense weapon.

"Susan" agreed to speak with affiliate KSDK, but wanted to remain anonymous.

"You stick your fingers through the eye holes of the cat, and the ears are used similarly to what a key through the fingers would be," she said.

The cat eye keychain is illegal in some states and Susan found out the hard way. She bought one after hearing reports of recent attacks on women. She says she forgot about the keychain until she was at the airport on her way to Mexico for vacation. That's when the TSA had some bad news for her.

"They told me carrying the cat eyes is similar to carrying a switchblade," Susan said. "It's illegal to even carry these things in public."

The woman was arrested and briefly detained by airport police. Now, she's facing criminal charges.

We checked with the Mecklenburg County District Attorney's Office. A representative there told us if the cat eye keychain is made of metal, it can be considered a type of metallic knuckles.

While it’s not illegal to own them, it is illegal to carry them concealed outside of your property. It's a class two misdemeanor, and the consequences can range from a fine to up to 60 days in jail.

High-profile celebrities like Lena Dunham have also found this out the hard way. Now with a legal battle looming, Susan has a warning for others.

"It would definitely not be worth the jail time or a fine for such a cute keychain."