Baby monitors shouldn't be used as a substitute for adult supervision. They should be considered as an extra set of ears—and, in some cases, eyes—that help parents and caregivers keep tabs on sleeping babies. Using one can alert you to a situation before it becomes serious, for example, if your baby is coughing, crying, or making some other sign of distress. Experts warn that you can't rely on a monitor to prevent Sudden Infant Death Syndrome (SIDS).
In addition to being untested for efficacy, physiologic monitors can increase both your stress and your baby’s stress with false alarms and unnecessary trips to the hospital. Dr. Christopher Bonafide, of the Children’s Hospital of Philadelphia wrote that parents are increasingly bringing healthy babies to the hospital over a false alarm, noting that changes that often set off a monitor are “just normal fluctuations.”
This is a light or beeping sound that lets you know that you've reached the monitor's range limit. If you have a model without this feature, static might be the only indication that you're out of range. (A monitor's range can vary due to your home's size, its construction materials, and other factors.) The greater the range, the better--especially if you plan to take your monitor outside.