A standard 3.3V GPIO can typically push something like 30 to 60 mW. You won’t get all of that as transmitted signal — it will depend on how well your random antenna wire matches the impedance of the gpio and the frequency. I’m really not sure the audio quality is going to be anything more than just intelligible, but I’d guess you’d get at least 10 mW or so of useful power, which means it should generally work within a small house.

No, I'm using this in my car just for a very short range (< 200mm)