Sounds like a fun project but, when WAF is on the line and living things W cares about, I'd just run a cable.

Running a cable is not impossible, but extremely unsightly. Would have to go around the house for almost 100 feet and it would be very visable. (My Wife stated, ABSOLUTELY NOT!)

 

In that case the relay circuit I posted is not needed assuming the transmitter can operate continuously over the time needed.
According to the specs it operates on 9 volts at 13ma so probably fine

Actually, with my design software, I was designing something quite similar. (Justed started it, so much is missing.)

 

I was just thinking back to the early days of my automated cold frame project. I built it so my wife could get an early jump on growing starter plants in March when the temps outside were still very cold and a bug in my code left the lid slightly open on a very cold night and nearly killed her plants.

I'm following this topic because I would like to add a wireless remote rain sensor to my Rainbird controller and it would need basically the same type of communication because running a wire would also not pass WAF

 

I was just thinking back to the early days of my automated cold frame project. I built it so my wife could get an early jump on growing starter plants in March when the temps outside were still very cold and a bug in my code left the lid slightly open on a very cold night and nearly killed her plants.

I'm following this topic because I would like to add a wireless remote rain sensor to my Rainbird controller and it would need basically the same type of communication because running a wire would also not pass WAF

Reminds me of when I retired. All the team said, awesome, no more boss! And I said, you forget, I'm still married...