I'm using a fairly basic home networking setup, and would like to know when it becomes unreachable due to electricity blackout or internet being offline. My idea was to use my raspberry pi to send out/or receive signals regularly, and when it doesn't, receive a notification/alert on my android phone.
Also, I would like to do this without opening ports and/or exposing my (dynamic) ip address if possible, and free if possible (but I'm okay with paying for a basic service too, as long as it's not too expensive).
How would one go do such thing?
EDIT: I'm not asking really for a step by step solution, just point me in the right direction on how to properly do this with suggestions of software/services, I'll try to find my way through there. Thanks in advance!