What would you do if you ..... (be) locked out of your house?

1. This sentence uses the second conditional structure (If + simple past, would + base form of verb).
2. The verb 'be' needs to be in the past tense form for the 'if' clause.
3. The correct form is 'were' (or 'was' in informal contexts, but 'were' is standard for hypothetical situations).