Baby, intercom and shabbat

Question

Have a new baby girl! have had this question for years! can i leave an intercom on in the baby's room and then the receiver in another room. Of course it will be set up before shabbat. and when an adult walks in the room - can we talk in the room ( because i feel like it would be like speaking into a microphone on shabbat) this may not be an issue for the newborn but what about adults thanks and shabat shalom ds