The most important thing to look for in all kinds of baby monitors is audio quality. Regardless of whether you want a video-based baby monitor or not, you need clear audio so you can hear your baby properly. You'll also want one with sound activation so that you don't have to listen to white noise 90% of the time. With sound activation, you'll only hear the noises from your baby's room when there's something important to hear.
Baby monitors may have a visible signal as well as repeating the sound. This is often in the form of a set of lights to indicate the noise level, allowing the device to be used when it is inappropriate or impractical for the receiver to play the sound. Other monitors have a vibrating alert on the receiver making it particularly useful for people with hearing difficulties.
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.