This is intended to be used with pfSense HACS Integration: GitHub - travisghansen/hass-pfsense: pfSense integration with Home Assistant . However it could be used with any device tracker that reports home when the device is up and something else when it isn't.
It will create a persistent notification when triggered.
Triggers / notifications can be enabled for a time period each day and/or for specific days of the week. There is also the ability to roll your own specific notification or other action as an action statement.
I also found that Awesome Blueprints Matt has a blueprint to send this stuff to your phone, so I referenced that here to be helpful if you are looking for that. If you want to send these notifications to a mobile device, i suggest you look at the following blueprint to use in conjunction with this blueprint. I am not affiliated with that, but decided I didn't want to re-invent the wheel as mobile HA is not something I do every day.

🐘 Requirements

Persistent Notification Integration Required

You must have this integration enabled on your system to run the automation, since the these notifications are generated by this integration. This should be activated in your HA Instance by default, so unless you tweaked the default configuration, you're good to go.

Persistent Notification Integration Docs

Community link for this blueprint

🗿Notice👮🏿‍♂️:

• Copies of the original Blueprint that were converted via the 'Take Control' feature or other means are officially not supported by me.

• I may or may not be able to support you when you have a problem after you make changes to my code, as some of the code is no longer mine.

• I & my license also require attribution as a link back to the original should you use this code in your own creation.

• Here is a link to my license & the original github post expected to be followed & referenced as attribution should you use this code elsewhere.