Why is deadlock alert not working? I created a deadlock alert including notification to an operator like this:

EXEC msdb.dbo.sp_add_alert @name=N'1205 Deadlock', 
        @message_id=1205, 
        @severity=0, 
        @enabled=1, 
        @delay_between_responses=30, 
        @include_event_description_in=1, 
        @database_name=N'myDB', 
        @category_name=N'[Uncategorized]', 
        @job_id=N'00000000-0000-0000-0000-000000000000';


This alert is registered for notification.

It's history says it never appeared although it is in place for months and there are multiple deadlocks per day. I created a deadlock manually. It shows up in the Log File.

What is missing for this alert to raise a notification? 
Other notifications like e.g. 18456 Invalid Login work fine.
Probably the error 1205 is not set up to be logged in ERRORLOG. Look it up in sys.messages:

SELECT *
FROM sys.messages 
WHERE message_id = 1205;


If the column is_event_logged is set to 0, change it this way:

EXEC master.sys.sp_altermessage 
    @message_id = 1205,
    @parameter = 'WITH_LOG',
    @parameter_value = 'true';


The documentation for sp_add_alert describes under which conditions an alert is raised:


  Remarks
  
  sp_add_alert must be run from the msdb database.
  
  These are the circumstances under which errors/messages generated by SQL Server and SQL Server applications are sent to the Windows application log and can therefore raise alerts:
  
  
  Severity 19 or higher sys.messages errors
  Any RAISERROR statement invoked with WITH LOG syntax
  Any sys.messages error modified or created using sp_altermessage
  Any event logged using xp_logevent