With my DD i didnt use one, our house was small and her room was next to ours and her window backed onto our backyard. With DS we used one as his room was down the other end of our new bigger house and i felt that i would not be able to hear him if he woke, we will use it again with this one, i picked it up on special from Coles its a fisher price and i payed $7 for it as it was clearance stock. However DD was the best monitor for me, she would come and wake me to tell me DS was crying......lol