Few days ago Nokia released an update called the Nokia Accessories update to all the WP8 Lumias bringing some improvements in monitoring the battery status when the device is connected to a charger/usb or fatboy pillow. Most importantly this update brings the Sleeping screen feature in the Nokia Lumias.
But this sleeping screen is not the same as some of you might have already tried on your Symbian^3 handsets or on N9, which always appears and shows info on the screen whenever you locks your phone (almost like a screensaver). The sleeping screen on lumia only comes when you dock your device with an NFC enabled accessory like the Fatboy wireless charging pillow, JBL Power-up, etc.
Once connected to an NFC enabled accessory, a screen like the one shown in the image above appears on the screen showing a big digital clock, weather info and the battery status with an occasional movement.