The Nanit Swaddle was designed for babies sleeping on their backs only. If your baby is already rolling over from back to tummy, you can use the Breathing Band which allows monitoring Breathing Motion of babies sleeping on their back or tummy.
It is also important to note that to monitor Breathing Motion you need to use only one Breathing Wear item at a time. (Either the Nanit Swaddle or the Breathing Band) For best results, don’t use Breathing Wear on thick fabrics and make sure your crib’s sheet are solid colors.