LullbeeA glowing rectangle is the opposite of a wind-down. Even at minimum brightness, a lit screen in a dark nursery is often the brightest object in the room, and it sits exactly where curious eyes go. Sleep sound is supposed to remove stimulation, not add a night light with a user interface.
Light is a signal
Darkness is one of the strongest sleep cues the body gets, for babies and for the adults rocking them. A dim, warm, boring room says the day is over. A bright cool-toned screen says the opposite. Whatever is playing, the room does better when nothing in it is glowing.
What screen-off playback means
The sound keeps playing when the phone is locked and the display is completely dark, for as long as it is needed, without the app being open on screen. That is a technical capability an app either has or does not. A video playing on a propped-up phone does not qualify, and neither does a website that stops when the browser sleeps.
Setting the room up
Phone across the room, face down or screen off. Do-not-disturb on. Volume at the soft-shower level. If a little light is genuinely needed for feeds, a separate dim warm lamp beats the phone screen every time, because it can point away from the crib.
Lullbee plays entirely with the screen off, and its fade-out timer ends the night silently, no tap, no glow, no checking.