Cpu-Alert in SQL Server -2012 standard edition
Have you tried the DMV sys.dm_os_performance_counters ? Using this view you can get several perf. counters, where you can sample by intervals to have an idea how your system is going. 

This is the documentation by Microsoft: https://docs.microsoft.com/en-us/sql/relational-databases/system-dynamic-management-views/sys-dm-os-performance-counters-transact-sql

Here you can find a few examples how to use it:
http://www.sqlservercentral.com/articles/Performance+Tuning/71784/

And here is an example how to get your current CPU usage: 

select perfCount.object_name
     , perfCount.counter_name
     , CASE 
            WHEN perfBase.cntr_value = 0
            THEN 0
            ELSE (CAST(perfCount.cntr_value AS FLOAT) / perfBase.cntr_value) * 100
      END AS cntr_Value
FROM
    (select * 
        from sys.dm_os_performance_counters
        where object_Name = 'SQLServer:Resource Pool Stats'
          and counter_name = 'CPU usage %' 
     ) perfCount
inner join (select * 
            from sys.dm_os_performance_counters
            where object_Name = 'SQLServer:Resource Pool Stats'
            and counter_name = 'CPU usage % base'
            ) perfBase
ON perfCount.Object_name = perfBase.object_name