A security system unlocks a locked state, which limits a use of a vehicle device attached to a vehicle, by inputting a preset genuine password. The security system may generate key information by converting the genuine password based on a predetermined rule. The key information is used for generating an alternative password that unlocks the locked state instead of the genuine password. The security system may generate the alternative password based on the key information. The security system may unlock the locked state when the alternative password is input.