Thank you for reaching out to the Samsung community! We would like to inform you that Demo Mode is a utility setting that has been designed for developers in android 7.0 Nougat. This mode is usually enabled for taking screenshots as it replaces the notification bar with a generic. It does not display the notifications and low battery warning which usually appear at the top panel of the phone screen which usually shows notifications icons, alarms, low battery warnings etc.
Be sure to hit ♡ when you find an answer that works for you. For Further assistance, you can get in touch with us via Live Chat option by following- http://livechat.support.samsung.com/Customer_new/IN. You can also connect us via Samsung Members web community by following mentioned url-https://community.samsungmembers.com/en_IN#/
