I was told it is compatible with ipod touch and up. I bought fitbits for 5 out of 6 grandchildren. # 6 was into other things - like snowboarding.
The older 4 had compatible smart devices. The 8 yr old girl was a little young for an upgraded smart device - so her mom gave her options of using mom's iphone or the family ipad for now - and she was happy with that. She'll probably get a compatible device of her own next year.