Caleb Kenyon, a defense attorney in Florida, saw a geofence warrant was when a new client received an alarming email from Google in January 2020. Police were requesting personal data from the client, Zachary McCoy, and Kenyon had just seven days to stop Google from turning it over, the email said. The geofence warrant included a map and GPS coordinates, and instructed Google to provide identifying information for every user whose device was found within the radius of that location at a certain date and time. "It was so bizarre that I just didn't even have a concept for what I was dealing with," he said. Kenyon is not alone. As tech firms build ever more sophisticated means of surveilling people and their devices " technology that law enforcement is eager to take advantage of " the legal community is scrambling to keep up. The National Association of Criminal Defense Lawyers (NACDL) ... recently created the Fourth Amendment Center, named for the constitutional right against unreasonable searches. The center is one of the few resources available for helping attorneys better understand how new technology is being used against their clients. It can be years before the defense community catches wind of the newest surveillance tools. Unlike other search warrants, geofence warrants don't require probable cause or a specific suspect in mind; they gather information on anyone within the vicinity of an alleged crime. Advocates argue this violates the fourth amendment.