That depends on the type of keychain. Impact keychains, such as Kubaton-style models, are not allowed in carry-on luggage but can be carried in checked baggage. The same rules apply to knives or any type of stun gun. Keychains with an alarm can be stored in checked or carry-on luggage.The rules governing pepper spray are a bit more complicated. While no pepper spray keychains are allowed in carry-on luggage, you can put them in checked luggage provided they meet the necessary requirements, including a safety mechanism on the canister to prevent accidental discharge, and they meet both size and concentration requirements. For further information, check the TSA website.