Sound devices relay what is happening in baby's room via sound only. A great sound option is quiet unless the baby is making noise so that you won't be disturbed by white noise or constant static. This basic monitoring type can be all you need if your goal is being alerted when your baby is crying and needs your assistance. This style can be elementary with sound only like the V-Tech DM111 or it can have bells and whistles like a nightlight, 2-way talk, lullabies, and mic sensitivity adjustment features like the Philips Avent DECT SCD570/10. Most parents can get by with a sound only device as it provides the information you need to determine if your baby needs you or not.
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.