Final answer:
Alerts for new devices joining a home network come from router settings or security software and are vital for the security of the network.
Step-by-step explanation:
Devices that alert you when a new device joins your home network for the first time are typically managed through your router's settings or through specialized security software. This feature is crucial for maintaining the security of your home network as it allows you to monitor and control which devices have access. When a new device connects, the system can send you a notification, often via email or a mobile app, so that you can authorize the device or investigate further if it is unrecognized. The effectiveness of these alerts in protecting your home network from unauthorized access underscores the importance of having a robust home network security plan.