If you lock your device, turn it off, or exit the camera function, your device will no longer perform as a Wi-Fi video camera. To make the screen go dark, select “Dim Screen” at the bottom of the display. The camera will still run, but the screen will appear dark. Tap the screen once to re-enable it.
Since the device is always on, be sure to keep it plugged into power. Also, consider enabling “Do Not Disturb” mode in your settings.