this one actually works on fitbit Charge 3 . Thanks IchibanNeko the flashing at night was driving me nuts
1) From the clock face screen, long press the haptic "button" on the left of the C3. The device should vibrate and show a screen with two options--Screen Wake at the top, and Notifications at the bottom. (If you have a special edition model with Fitbit Pay, the payment screen may show first instead. In this case, swipe left to get the above options.)
2) Touch the Screen Wake light bulb icon so it grays out with a diagonal line through it. This will keep the screen off with wrist movement.
Note that the C3 screen is designed to wake on a double tap regardless of the Screen Wake setting (like the Charge 2), so if you thump the arm with the C3 in just the right way (not necessarily a factor of strength), it can wake the screen. For example, I've had my screen come on when clapping my hands, or tapping a spoon on a dish. Just something to keep in mind.
