A baby monitor is system that allows you to hear or see your baby when you are in different rooms. The most commonly used monitors are sound monitors but there are also visual monitors with which you can watch your baby on a screen, respiration monitors which check the baby's breathing and child alarms which will warn you if your child is wandering off. If you live in a small house or flat and can hear your baby easily wherever you are then you won't really need a monitor. If the distances between the room your baby sleeps in most and other rooms in your house are greater then a monitor will reassure you that all is well. TV monitors allow you to watch your baby on screen and can be used as simple sound monitors when a picture is not required.
Units are either mains or battery operated.
Battery operated monitors are entirely portable. Some come with rechargeable batteries which can save the expense and fuss of new batteries, others come with adapters for optional mains use. Features may include an optional alarm that sounds when no movement is detected for more than 20 seconds. These monitors will either reassure you greatly or terrify you half to death. Most new parents worry a great deal about their baby's breathing.