The best device for keeping in close contact with your infant is the Classic Analogue Baby Monitor. As the volume of the sound emanating from the baby unit grows, the parent unit's LED strip gradually illuminates. If voice activation is enabled, the baby unit must detect sounds before the parent unit will turn on. To guarantee communication between the two devices and lessen interference, two channels are offered. Both the parent and kid units run on batteries (the parent unit comes with three AAA Ni-MH rechargeable batteries) or an AC adaptor (two provided).