済 ON: サイ, セイ KUN: す.む, -ず.み, -ずみ, す.まない, す.ます, -す.ます, すく.う, な.す, わたし, わた.る settle (debt, etc.), relieve (burden), finish, come to an end, excusable, need not
For code-type locks that don't need a key, there are 'free dial' systems where you can set any number you like, and fixed types where the number is set in advance.