If you’re a U.S. citizen: CBP cannot deny you entry to the United States merely because you refuse to unlock the phone. If you’re a non-citizen seeking admission: refusal is much riskier.

The important wrinkle is that CBP’s published policy expressly guarantees that a person being admitted as a U.S. citizen won’t be denied entry solely because CBP couldn’t inspect the device. It doesn’t give lawful permanent resident (green card holders) that same explicit statement. Instead, it says refusal by a “foreign national” can be considered in an admissibility determination.