Well from what the book says you set it at the highest temp you want it to go beyond your temp setting.If it reaches that temp or beyond it will sound your high temp alarm.The same goes for low temp.So basicly if you set it at 90 for the highest you want your incubator to reach and it goes past that.It will sound that alarm. I have not programed that part as of yet so i cant give my input on how it works.It also has night cycle if you choose to use it.