The goal is to monitor land-mobile radio systems. These are the systems used by ambulances, police cars, construction crews, and pilots. Because these transmissions travel through the public airwaves, they can be intercepted by anyone with the right equipment.
Historically, these devices were synonymous with "police scanners," but modern technology has expanded their reach to include everything from maritime communications to amateur radio (Ham) bands. How Radioscanners Work: The Basics radioscanner
In many jurisdictions, it is legal to own and listen to a radio scanner. However, laws vary significantly regarding: Using a scanner inside a motor vehicle. Listening to encrypted communications (strictly illegal). The goal is to monitor land-mobile radio systems
While the stereotypical image of a "scanner" involves a detective sitting in a parked car, the reality is far more broad. Today’s radioscanners are sophisticated pieces of technology used by journalists, hobbyists, and weather enthusiasts alike. Listening to encrypted communications (strictly illegal)