Orin Kerr has this interesting post at The Volokh Conspiracy. It begins as follows:

There has been a lot of press coverage recently about a search warrant obtained in Los Angeles allowing the government to force people present when the warrant is executed to press their fingers and thumbs on the fingerprint sensors of any phones or computers found there to unlock them. A lot of people have wondered: Is that legal? I don’t think there’s an easy answer to that. Here’s an overview of some of the legal issues.