Some audio/video monitors filter out "normal" sounds and motions. The receiver is supposed to turn on only when your baby makes an unusual motion or sound, such as crying or rolling over when he's waking up from a nap. This feature is designed to extend battery life, although the receiver should be docked for overnight monitoring to keep the battery charged. We haven't tested any models with this feature, so we don't know how well it works.
If you sleep in the same room as your baby or live in a small enough space that you can always hear or see what your baby is up to, you probably don’t need a monitor. Otherwise, most parents enjoy the convenience a baby monitor provides—instead of needing to stay close to the nursery or constantly checking on your child, you’re free to rest, catch up on Netflix or get things done around the house during naptime. Monitors can also double as a nanny cam to keep an eye on your child and their caretaker.