A classic baby monitor is a device designed to monitor a baby using sound. It provides parents with an audio transmission from the child's room to the parent unit, allowing them to monitor whether the child is okay or needs attention. This device usually includes an audio input, microphone and speaker for both units and can function as a one-way communication where the parents listen to the child, or a two-way communication that allows the parents to talk back to the child. Traditional baby monitors are simple and reliable but do not have video transmission.