By design, the screen is blacked out to prevent the battery draining from the lit up screen, to prevent children from wanting to play with it, and to prevent accidental alterations to the programming which could render the device useless.
When the device is plugged in you will see the message on the screen: "Screen will black out when unplugged. New User? Download AngelSense app on your mobile to get started."
If a situation requires that the screen must be unlocked, a customer care agent will assist you.