Many parents prefer digital baby monitors to the analog type, because digital technology tends to block out interference from nearby electronic devices. One of the most basic types of digital monitors is the audio type, which features sound only and allows parents to hear their baby when they are in another room. Some monitors feature both sound and video, permitting parents to hear and see their baby so they know the child is safe. Another digital tool that can reassure parents is the movement monitor, which sounds an alarm when it does not sense movement after several seconds. This is often considered best for babies with sleep apnea or increased risk of sudden infant death syndrome (SIDS).
A basic audio baby monitor transmits sound from the baby's room to the parents' receiver, provided it is within range. This often allows parents to hear whether their baby is crying, choking or simply awake and happy. Though analog monitors perform the same function, they tend to suffer from interference from nearby electronic items such as cordless phones. In addition, it is possible for neighbors to hear the audio stream of an analog monitor, because it uses a frequency band to transmit sound; a digital monitor encodes the signal. For these reasons, many parents prefer digital baby monitors, though they tend to be more expensive than the analog type.
Some parents feel safer being able to see what their baby is doing, rather than just listening in, so they may opt for a video monitor. This device usually includes sound, permitting parents to get a good idea of what their baby is up to despite being elsewhere in the house. In most cases, the camera is placed next to the crib and the receiver is placed on a surface in the room where the parents will be, allowing them to look at the screen for an image of the baby. Many digital baby monitors with video include night vision for a clear image in a dark room, and some feature two-way audio that lets parents talk to their baby through the monitor so they can soothe the child without having to enter the room.
There also are digital baby monitors that observe the movement of the baby, alerting parents with an alarm when the child does not move for about 20 seconds. This is often the preferred monitor for babies with sleep apnea, because they have a higher-than-usual chance of stopping breathing during sleep. In such cases, a doctor may loan a hospital-grade breathing monitor to parents, but these types of digital baby monitors also are available for purchase by parents worried about the possibility of their baby suddenly being unable to breathe. Many movement monitors also include sound and enable parents to turn off the movement sensor when they feel it is no longer necessary.