I don't use baby monitors after overhearing a heated argument of my neighbors over my own baby's....
BUT, I could not function without a Sleep Sheep for infants. I have grown to LOVE those so much. They clip to the outside wall of the crib and have several seattings...heartbeat and ocean are my favorites and work like a dream.
After they are out of a crib, I turn on a ocean sounds cd on autoplay so it just repeats, over and over.