Build a radio beacon with the material found in the house at a cost of few euros.
We start with the idea that digital radio audio signals can be recorded and then decoded. Among my videos you can see how to decode a digital signal found on youtube.
You can use countless software and protocols. Important is that you can generate the signal, transmit it with a radio transmitter, receive it with a radio and record it here. Then this audio will be retransmitted.
Below are some low cost examples:
1. FM Radio Beacon
2. AM Radio Beacon
3. Multi Channel Radio Beacon AM & FM
If you plan to
use this system standalone you can associate an additional power
generator (solar panels, wind power generator, hydro turbine, etc)