I have owned and lost three fitbits, the last one a fitbit one. :/ I LOVED it - the sleep tracking feature is awesome - but I am no longer allowed to buy one.
(The last one lasted me.... 4 weeks? Longer than the other two, which I bought/quickly lost a couple years ago.)
The fitbit one has a molded silicone clip to hold the device. It's an improvement over previous models, but apparently still not super secure. Or it's possible I'm just exceptionally bad at keeping track of things on my person. (All three times, they were clipped to my pants.)