The "border search" exception to the Fourth Amendment's warrant requirement allows "routine searches" at an international border without a warrant or any suspicion. A couple of weeks ago, we told you about United States v. Williams, in which the Tenth Circuit declined to decide whether reasonable suspicion is required to conduct a forensic search of a person's laptop seized at an international border. The Court held that Mr. Williams would lose either way, because there actually was reasonable suspicion to search his computer.
Other courts have held that suspicion is required to support a search of a phone or laptop at the border. Recently, in Alsaad v. McAleenan, a Massachusetts district court held that suspicionless searches of personal electronic devices seized at the border violate the Fourth Amendment. The court emphasized that the border search exception is based the need to discover contraband in violation of customs and importing rules at the border, not to search for general evidence of crime. The court held that both a basic search of an electronic device and a more advanced (or "forensic") search are "non-routine" searches at the border, and thus require reasonable suspicion. But the court rejected the plaintiffs' argument that the higher probable-cause standard must be met.
Note: because Alsaad is a civil case, it does not deal with the good-faith exception that can be an additional obstacle in a criminal case in this developing area.