After you log into the Alert Labs Dashboard, click Menu in the top right of the page.
Select Notification Settings.
From this page you can customize how and when you receive alerts about your sensors. Make sure that the notifications you'd like to receive are in the on position (blue circle on the right - see example below).
Click the "Save Changes" button at the bottom once you're satisfied with your new notification settings.
Note: Even with notifications turned off, events will be logged in the "Event History" in the sidebar of your Dashboard. You may review events there at any time.