A doorbell is a signaling device installed near the entrance of a building, typically used to alert occupants of a visitor's presence. When pressed, it activates a chime or sound inside the home, letting residents know someone is at the door. Doorbells can be wired or wireless, with wireless versions often powered by batteries. Modern doorbells may also include features like video cameras and intercom systems, allowing homeowners to see and communicate with visitors without opening the door. These advanced models are often referred to as smart doorbells and can connect to smartphones for remote monitoring.