Scan the devices connected to your WIFI / LAN and alert you the connection of unknown devices. It also warns if a "always connected" device disconnects. In addition, it is possible to check web services for availability. For this purpose HTTP status codes and the response time of the service are evaluated.
During the manual install process... (I was installing onto an existing pi-hole installation) I had to install cryptography
pip3 install cryptography
before
python3 ~/pialert/back/pialert.py update_vendors
would run