This add-on lets your visitors save the search criteria and then notify them when a listing is available matching that criteria.
After installing and activating, you will see a settings menu as below.
Setup the above settings accordingly and now when a user will search and there will not be enough results, the following form will be displayed.
Site Administrators can access all the saved searches from WP Dashboard -> Real Estate Manager -> Saved Searches. They can see the criteria and also the email address of the visitor. Visitors can manage their saved searches from frontend using the shortcode [rem_saved_searches]