My husband and I have discussed this for a while before our boy was here as he thought we needed one of those and I was not so sure about it.
We decided to order one and see if we needed it. At first our baby was sleeping in our bedroom in a little rollaway bed next to ours. After almost four month he was sleeping through the night most times and we moved him into his nursery, which to my surprise worked without any hick ups. We used the monitor for a few days but the crackling noise it made just kept me awake so we decided to turn it off and see if we could still hear him. That worked out fine so we just keep the bedroom doors open since then and returned the monitor.
Do you use one of those monitors? What made you decide for or against it?