although it may seem expensive, it can save the life of your baby! (Be careful however, that does not prevent sudden infant death), for one, the alarm went off a couple of times: my baby systematically turned on his stomach and put his head in the corner of the bed, which prevented him from breathing because of the bed tower ... While the alarm sounds on both the parent unit and the baby unit, but I think it is just to wake the baby, to react and that changes position. the sound is adjustable, as is the sensor sensitivity. you can program a minimum and maximum temperature alarm for the nursery; there is an alarm for the battery level of the parent unit.