The point of numbered locks? Using these instead of a regular padlock means that you can easily find out if your partner has been tampering or trying to manipulate the chastity device they're in.

These locks are designed to easily detect tampering.
They are single use, numbered, and can't be reused once removed. The numbering allows you to know if they've managed to remove one lock and replace it with another.
They are also lightweight and water-safe.