It is firmly established in case law that when a suspect is arrested, their cell phone cannot be searched without a search warrant, subject to some very narrow exceptions. However, the rules regarding cell phone and laptop searches at the border are much less restrictive.

The most common way CBP (Customs and Border Patrol) obtains access to cell phone and laptop data is through consent. If an agent wants to look in your cell phone or laptop, they may simply ask for your permission.

For laptops, CBP can do a “quick look” into the laptop without any reasonable suspicion of criminal activity. This means they can turn on the computer and briefly search through what is on the computer. If CBP wants to keep the computer and subject the computer to forensic inspection, they only need reasonable suspicion that the laptop contains evidence of criminal activity. This is far less than the standard that traditional law enforcement would have to prove in the same situation, which is probable cause.

Federal courts have been presented with several cases involving electronic device searches at the border and so far, courts have held that CBP’s broad search authority extends to electronic devices, with the exception of “forensic” searches, which are done by specialists in order to gain access to hidden or password protected files.

However, CBP has issued a policy directive, which gives a bit more clarification. The directive reiterates that agents have the constitutional authority to search electronic devices. If a device is password protected, and agents are unable to perform the basic search of the device agents could hold the device for a period of days, with supervisory approval. Although technically there is no level of suspicion required to do this, the requirement for supervisory approval should ideally help to ensure that devices are not kept arbitrarily.
(https://www.cbp.gov/sites/default/files/assets/documents/2018-Jan/CBP-Directive-3340-049A-Border-Search-of-Electronic-Media-Compliant.pdf)

Additionally, this policy directive specifically addresses the special procedures that agents should follow if a traveler claims that information contained in an electronic device is protected by attorney-client privilege.

Travelers entering the U.S. with electronic devices should be mindful of CBP’s relatively broad authority to search these devices. If you have any questions regarding the legality of a CBP search, you should speak with a licensed attorney.