There are several ways to do this. I guess the Photon board would work, but $29 seems a bit pricey - and a B-O-R-I-N-G project.
Here's how I might do this if it were my project:
First - an email alert is useful (if I'm out), but I wouldn't depend on it to wake me from a sound sleep. I want an annunciator for when I'm in the house, and email when I'm not - I want both of these alerts.
Second - I don't want a battery-powered RPi as part of the solution - more complexity, less reliability & more expense. Instead, I'll use a "2nd RPi" (or any PC/device with a network stack) to monitor the "basement RPi". One simple way to implement the event detection software is:
2nd RPi will periodically
ping basement RPi
if basement RPi fails to respond
then 2nd RPi activates alarm & sends email
This may be implemented in Python, a shell script - or virtually any other programming language. And obviously this scheme requires both RPi's to be connected to a network.
Third - send an email message from the 2nd RPi (or PC/whatever). Again, several platform-dependent ways to do this, but here's one way that uses RPi's
mail program, a
GMail account in a simple Python script..
Fourth - trigger the annunciator/alarm from the 2nd RPi. This is the interesting part: When I think of a hard-to-ignore annunciator, I think of a smoke detector - those little white pucks mounted on the ceiling or wall in every house. Since all we need is the annunciator, it's not necessary to have a new smoke detector. In fact, the sensor components are not needed at all as the annunciator will be activated via the "push-to-test" contacts.
As with all things, there are YouTube videos that illuminate the way... I didn't have time to find a good YT video; this one covers the essentials of the push-to-test hardware in a small fraction of the total run time.
The event detection software described above will do two things once it has detected the "basement RPi" isn't responding:
- Send the email
- Set a GPIO pin
The GPIO pin will actuate the annunciator through a hardware interface - a relay, or a transistor switch. There are numerous Q&A here that explain this (one example)
Finally - This is only an outline - an approach if you like - to meeting your requirement. It's an interesting project IMHO - you'll have learned a lot when you complete it. You may have specific questions as you work your way through the project. We'll try to help with those also.