Blue Tooth2. If your almost flat footer or are flat footed I HIGHLY recomend these flip flops, if you havent found the right kind yet. I still give the sandals 4 stars because they do feel like they are comfortable if I could size up maybe to an 8. I am please at the amount of stress the closet organizer has taken off me. very portable extremely easy to use. As a result they rubbed at the heel especially. I have about 25 pairs of FitFlop and love them. Liked them so well I bought again My family jokes that I think they are "one use disposable" and they KNOW to not loan me a pair. Now for me its not entirely invisible under my clothing.