I’m surprised nobody has mentioned the simplest version:
\d
This will match any digit. If your regular expression engine is Unicode-aware, this means it will match anything that’s defined as a digit in any language, not just the Arabic numerals 0-9.
There’s no need to put it in [square brackets] to define it as a character class, as one of the other answers did; \d works fine by itself.
Since it’s not anchored with ^ or $, it will match any subset of the string, so if the string contains at least one digit, this will match.
And there’s no need for the added complexity of +, since the goal is just to determine whether there’s at least one digit. If there’s at least one digit, this will match; and it will do so with a minimum of overhead.