Short answer

Don't carry your seed phrase across borders if you can avoid it. US Customs and Border Protection (CBP) has the legal authority to inspect electronic devices and physical documents at the border without a warrant, and seed phrases visible during inspection can lead to forced disclosure, device seizure, or worse. The same applies in reverse — entering some jurisdictions with crypto seed material may run afoul of capital-control laws. The right answer: keep the seed phrase at home, restore from seed only if you actually need to access crypto while traveling.

The US border-search rules

CBP's authority at the US border is broader than law enforcement's authority within the US. They can inspect electronic devices (laptops, phones), demand passwords, and seize devices for forensic analysis — all without a warrant. Recent court decisions (Alasaad v. McAleenan, 2019) reaffirmed this authority.

Physical documents in your luggage are equally subject to inspection. A piece of paper labeled "Bitcoin recovery phrase" with 12 words is straightforward for an officer to identify. Whether they take action depends on the officer, the context, and any flags on you (travel patterns, declarations, etc.).

What CBP can do with your seed phrase: photograph it, demand more information, refer to other agencies (FBI, IRS), or in extreme cases hold you for further questioning. They cannot directly seize crypto on-chain — the seed phrase alone doesn't authorize CBP to move funds — but the information they collect can lead to follow-up enforcement.

Other-country border rules

Significant variation. Some countries (Russia, China during certain enforcement periods, North Korea obviously) have explicit prohibitions or restrictions on cross-border crypto. Some (Singapore, Dubai, Switzerland) are crypto-friendly. Most Western countries are similar to the US — broad inspection authority, discretion to act.

If you're a US holder traveling to a crypto-restrictive jurisdiction, the safer assumption is that crypto-related materials in your possession could be flagged or seized.

The practical recommendation

Don't carry the seed phrase. Period. Keep it at home in a fireproof safe or bank safe-deposit box. If you need to sign transactions while traveling:

  • Bring a hardware wallet without the seed phrase. The hardware wallet's PIN protects access; the seed phrase stays home.
  • Use a phone wallet with a small "travel float" — under $5K is acceptable risk.
  • For larger holdings, plan to not transact while traveling. The CEX accounts work via web; the offline wallet sits at home.

If you must carry the seed phrase (extended international relocation, etc.): Shamir-split it into 3 parts, carry only 1 part (others stored elsewhere). Carrying 1 of 3 shares conveys no information by itself.

The "encrypted file" option

Some holders carry an encrypted text file containing the seed phrase on a USB drive. CBP can demand passwords for encrypted devices at the US border. The encryption alone is not protection against compelled disclosure.

For US persons, there is some Fifth Amendment protection against being compelled to provide encryption passwords, but the case law is mixed and depends on whether the contents are "foregone conclusion." This is not a legal strategy to rely on at the border.

Bottom line

The seed phrase should never be in your possession during border crossing if you can avoid it. The setup that requires you to carry it is poorly designed; replace it with a structure that doesn't.

Further reading: Mnemonic, Five ways to store a seed phrase.