Wireless doorbell transmitters and receivers
These are common in large distributors like Banggood.  They use a simple shared f so connect as many of the same as you want.
Anecdotal
I installed one about a year ago and the Rx twin C cells died and the Remote CR2032 is such a low power Tx, that I would only believe Operating at 300 m range, is fictitious best case with wall reflectors pointing in the right direction without obstruction. I got 3m only thru the front door frame.
As it was the Rx could only pick up the Tx near the front door Tx with Rx just inside the front hall and not in the kitchen or den. The speaker was so puny , it was barely audible with some background TV noise.
So I modified it.
Added 0.5 m magnet wire to CR2032 gnd along exterior door frame to act as an antenna. This made it work anywhere inside the bungalow.
A big improvement would be a hidden lithium manganese dioxide cell as large as the Tx and button.
Put Rx inside a large plastic coffee container and added a 5” speaker on top instead of lid using AWG magnet wire. Then hid it behind a cabinet. Now we could hear it inside , but not outside.  Good enough. Replaced C cells with the best Panasonic Alkaline cells. The door bells are hardly used, so it is 10y shelf life I am hoping for.