The Kidde Detect Smoke Alarm 4 Pack is a set of hardwired interconnected smoke alarms with backup batteries included. Each alarm is from the Kidde 20SAR model, ensuring quality and reliability. These alarms offer added security with their interconnected design, so if one alarm detects smoke, all alarms will sound to alert you and your family. With a power source of hardwiring and battery backup, you can rest assured that your home is protected even during power outages or battery replacements. Easy to install and maintain, this smoke alarm set is a crucial component of any home security system.