In the latest battle for investigative techniques to defeat password-protected smartphones, federal prosecutors have begun including in search warrants not only personal phones (“dwelling contents”) at a location subject to search but also the fingerprints of the occupants. By doing this, authorities may be able to access the data stored on the phones found at a residence, since the warrant can compel ALL occupants of a dwelling to surrender their fingerprints and, by extension, use them to unlock their phones.

An example of this approach was recorded in May 2016, when the Department of Justice sought to search a Lancaster, California, property. As reported by Forbes magazine, a memorandum about the warrant described the request as “Authorization to depress the fingerprints and thumbprints of every person who is located at the SUBJECT PREMISES during the execution of the search and who is reasonably believed by law enforcement to be the user of a fingerprint sensor-enabled device that is located at the SUBJECT PREMISES and falls within the scope of the warrant.”
This example differs from the case in which Apple was asked to unlock a personal phone, because the dwelling and, by extension, its occupants were being covered by the search warrant. In the Apple case, it successfully argued that since Apple wasn’t under suspicion, being compelled to unlock another user’s phone without a warrant could lead to an invasion of customer privacy.

It’s already common for search warrants to include personal phones as contents of the dwelling. With fingerprints included as well, law enforcement has a tool to achieve access and can therefore compel the occupants to make the phones accessible by law.

Whether this technique will stand up to scrutiny remains to be seen. Digital privacy groups such as the Electronic Frontier Foundation have expressed concern, but the courts have yet to take up the issue. The final test for this access mechanism will arise when a case goes to court and a defense attorney is able question the legality of the evidence gathering.