The extra mode for cities allows you to dull your sensor to avoid picking up false alarms common in more populated areas.
While some radar detectors are only able to sense radar ahead, others are able to detect radar behind you as well.
Some police use radar detector detectors (or VG-2). Radar detectors with a VG-2 alert can recognize when police are using the VG-2 and then shields or shuts down your radar detector.
Different radar detectors alert you in different ways. Some produce audible beeping, while others flash a light to alert you to the radar detection. Some detectors do both.
Detection Bands
X Band, K Band, Ka Band, Laser
Muting allows you to turn the audible alerts off, while maintaining a visual alert.