Enabling SMS alerts means a text message will be sent to your mobile phone with monitoring status alerts.
Enabling SMS alerts:
Click on the drop-down menu next to the account avatar in the upper, right-hand corner of the dashboard.
Click Global Alerts and then SMS.
Enter the mobile number, choose your mobile service provider and then click Add Phone.
If you are still not sure what do, please feel free to open a support ticket with the Sucuri team.