In recent posts, we’ve been looking at the topic of facial recognition technology as used in law enforcement. As we noted last time, critics of the technology argue that its use may raise constitutional issues. In this post, we wanted to say a bit more about that.

It is certainly not unprecedented for emerging law enforcement technologies to raise constitutional issues, particularly under the Fourth Amendment. Another technology that has raised similar questions is a form of radar which allows law enforcement to send signals through a device attached to the wall of a suspect’s home to take a look inside the home. Law enforcement agencies have been using this technology for some time now, even though it poses potential problems under the Fourth Amendment. 

The U.S. Supreme Court, which has the final word of authority on interpreting the Fourth Amendment of the U.S. Constitution, ruled in 2001 that law enforcement may not use thermal imaging devices to scan the exterior of a home without first obtaining a warrant. A similar decision in 2013 essentially set forth the same rule.

One of the legal concepts that comes into play in these cases is “reasonable expectation of privacy,” which refers to whether or not a reasonable person would expect that he or she was being watched or heard by the public. In one’s own home, of course, one enjoys special privacy protection, whereas there is less protection in a motor vehicle, and even less walking out in the open. When law enforcement violates a reasonable expectation of privacy, it is considered a search for purposes of the Fourth Amendment and a warrant is, therefore, required, unless certain exceptions apply.

In our next post, we’ll say more about how the Fourth Amendment can come up in the context of criminal defense, particularly with respect to protections available to criminal defendants.