How to send an email to the admin when user fails to login? I need to implement the functionality to notify the admin user via email whenever someone fails to login entering wrong password. Basically simple email format containing the username for failed account to login. Can someone give guidance or suggestion?

P.S: I checked the Rules module but it doesn't have required Rules event like "When user fails to login".
People mistype or use wrong alternate passwords all the time. Would be overkill to send e-mail on a first failed attempt. 

For security reasons, Drupal blocks user account after 5 login failed attempts.

You can use Rules Block/Unblock User to send e-mail when user gets blocked. (failed 5 times)


  This module adds rules events, as well as some default rules, for when
  a user account is blocked or unblocked.