You can self-host these open source apps that will regularly scan the devices connected to your WIFI / LAN and alert you the connection of unknown devices. Pi.Alert has a few extras like warning of the disconnection of “always connected” devices, additional notification options, presence history, and others I show in the video.

In this video I compare these two apps and show what they look like in action, as well as covering some tips and solutions for issues I had experienced.

Intro 00:00
Comparison 01:45
Resource Stats 08:47
E-Mail Alerts 10:36
WatchYourLAN Interface 11:11
Pi.Alert Interface 12:35
Device Details 13:08
Scanning a Device 17:06
Presence History 19:07
Events 19:15
Network View 19:19
Maintenance and Settings 19:31
WatchYourLAN Docker Compose 20:39
Pi.Alert Docker Compose 23:03
Pi.Alert Config File 24:32
Find Network Interface Name 27:01
Mobile Interface 28:08
Wrap Up 28:58

Reference Links:
Pi.Alert website: