Different databases have different methods for subscribing to search alerts. Thankfully, a large number of databases are owned by a few large companies. The company or vendor typically uses one interface for the databases they offer. Most of these vendors will permit users to create search alerts across a number of databases by simply creating an account on the vendor website.
This guide lists 4 of the most prominent vendors that offer search alerts in conjunction with their databases. Each tab will provide information on setting up an email alert and/or RSS Feed.