Open Performance Monitor, expand Data Collector Sets. Right-click User Defined, select New and then Data Collector Set.
Give a name and then select Create Manually. Click Next.
Choose Performance Counter Alert and then click Next.
Click Add to select the counter you want to monitor. Click OK
Now specify the limit so the alert could be triggered. Click Next.
Specify an account with privileges needed to collect the information. Click Finish.
If you want to configure to execute a script when the alert triggered, then right-click the Alert and select Properties.
Select the Task tab, and configure what you want to execute when the alert will be triggered. Click OK.
To start the Alert, right-click it and select Start.