The transmitter, equipped with a microphone, is placed near to the child and the receiver equipped with a speaker, is carried by, or near to, the person caring for them at the time. Some baby monitors are duplex (bi-directional), using transceivers that allow the caregiver to communicate back to the baby (parent talk-back), and some have a feature allowing music to be played on the transmitter (and thus played to the child).
One of the primary uses of baby monitors is when the infant is asleep in a separate room or floor, allowing caregivers or parents to keep track of any problems while away from the baby. For those worried about sudden infant death, a monitor should only be used under the supervision of a pediatrician or other doctor. Although commonly used, there is no evidence that these monitors prevent SIDS, and many doctors believe they provide a false sense of security.