Because I never managed to charge the device. And this happened not on one unit, but on two. The first device I received didn't charge at all - the light didn't even come on. So I returned this unit and traded it in for another unit which I have to admit worked slightly better than the first unit. At least this device had a charging light on. Sure, it stayed on for three days, but the device never charged. The sad thing is that this is almost the only budget wrist model on the market. I really wanted this to work, but it didn't work.
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