I'm 13, and I am wondering the if it would be legal to carry a karambit knife for self defense – in a sheath or folded. If laws for both are different, I would appreciate policies on both. If so, would I be allowed to conceal it, or would it have to be in plain sight? Any specific blade length limits?
Knife laws in the United States are notoriously ambiguous, often vary at the municipality level, and enforcement can best be described as capricious. I can't put it better than this eye-opening answer I found on Quora:
Don't ask anybody what the law is about knives. Not even the police. There's so much misinformation floating around out there.
Check the law yourself. Not just state law, but local law for any county or city you stop in or pass through.
I was tasked with writing a weapons policy for my security department, my former employer. I checked the Code of Maryland Regulations and found a mess. Knives are considered tools, not weapons, unless and until one uses or intends to use a knife as a weapon; knives are legal regardless of blade length; folding knives may be carried concealed, but fixed knives must be carried open; switchblades and balisongs are not OK, but no mention of gravity knives, locking mechanisms, or assisted-open mechanisms.
I carried my S&W assisted-open knife everywhere, including into Baltimore City several times. Then Freddie Gray was arrested for carrying one and died in custody. A whole lot of people thought the arresting officer had made an unlawful arrest, based on the state law, including the Baltimore City prosecutor … until someone bothered to check the city law and found that assisted-open knives are illegal in Baltimore City. The arrest was a good one. And I left my knife in my car from then on whenever I went into that town.
(I have on occasion asked police about knife laws. In every case the officer has declined to answer whether a particular knife or carry practice was legal.)