Ideally, the distance between the Lilypad and the Turtle does not exceed five (5) feet. Keeping the two in close proximity to one another ensures that the data connection between them remains strong. Placing the Lilypad next to the crib or bassinet (or wherever your baby is sleeping) is ideal.
The reason for this is rooted in parent comfort and baby safety. We use the lowest power bluetooth available in the Turtle, which means that the distance between Turtle and Lilypad while monitoring can't be much more than eight (8) feet before data gets too funky (and before you get too frustrated).