It has to be plugged into a usb port and that is not always convenient. I recommend this product to everyone. It?s fairly pixilated up close so minus 1 star. convenient Well made and my feet don?t slip to the top of the shoe when walking They are not only very reasonably priced, but, solidly built products and shielded nicely, not cheap feeling or looking. I will have them sewn back up but will never buy anything from the company who sells them. Very comfortable, supportive shoe. Hopefully it will last as long as my old pair of Yellow Box flip flops. So I told myself I wasnt going to rave about this unless I could go an entire week in below zero temperatures and still exit the shower with skin that felt supple and moisturized.