If you read the manual well and also understands, you can expand your system well .. I have a transmitter connected to the bell system and connect the power supply to the bell transformer. (Warning does not work with every bell transformer.) Then 3 more radio Gong spread in the house. The only run with batteries, has the advantage, you can depend on and take it where you can not hear the bell otherwise würde.Die batteries to last the part. The batteries in the transmitter are faster leer.Besonders when exposed to cold transmitter as the bell transformer is better.