If customs officials do take your devices, don’t make their intrusion easy. Encrypt your hard drive with tools like BitLocker, TrueCrypt, or Apple’s Filevault, and choose a strong passphrase. On your phone—preferably an iPhone, given Apple’s track record of foiling federal cracking—set a strong PIN and disable Siri from the lockscreen by switching off “Access When Locked” under the Siri menu in Settings.
Remember also to turn your devices off before entering customs: Hard drive encryption tools only offer full protection when a computer is fully powered down. If you use TouchID, your iPhone is safest when it’s turned off, too, since it requires a PIN rather than a fingerprint when first booted, resolving any ambiguity about whether border officials can compel you to unlock the device with a finger instead of a PIN—a real concern given that green card holders are required to offer their fingerprints with every border crossing.