Alerts are essentially a reverse search engine retrieval process. A web user creates an alert focusing on a keyword or keyphrase, and as the web crawler finds instances of that keyword, a notification is sent. Most alert systems only create a notification if the finding is new or matches a preset condition created by the web user. This subscription service can be vital for marketing agencies, SEO professionals, PR companies and brand managers. Alerts can be created for both search results and social results--depending on the need.