This button is only to sleep the terminal. When your side button of terminal isn't responding well, Please use this instead.
# Note: Before You boot this app for the first time after install , Please go to Settings-Security-Device Administrators and activate/give permissions to this app to lock your screen. If It says " Do you want to enable the device management function ? " , Please use to select the "Enable" . (This setting is to allow sleep terminal by this app.)