For future reference, there are apps that can detect help detect new network devices.

I have used the free “Fing” Android app that scans your network for devices, including IP/MAC addresses, and allows you to Confirm them as valid/known. If you later refresh the scan, the app will show any new devices (and allow you to confirm them also). Even if the previous devices go offline and online, they are not treated as new devices once they have been confirmed.