Touch Lock

Сенсорный замок прекращает непреднамеренное прикосновение к экрану, и он блокирует сенсорный ввод

Touch Lock stops unintentional touch on screen and it blocks touch input. It can disable the touch while watching youtube or movies. Also useful if you hand your phone to someone and don't want them to use your phone. It can useful to avoid accidental touch while calling in progress

Note :By Default MI does not support this feature. You need to enable it in settings. Please follow instruction in below link. http://www.gizchina.com/2014/09/09/fix-facebook-messenger-chat-heads-showing-miui-6/