Like it says in the article:
To use sys.dm_os_buffers as part of a monitoring process, you just have to look for the two events, RESOURCE_MEMPHYSICAL_LOW or RESOURCE_MEMVIRTUAL_LOW. These are available in the ResourceMonitor/Notification property within the XML. They are an absolute indicator of a low memory condition on your machine, so if you get the alert, you were low on either external/OS/physical memory, or internal/SQL Server/virtual memory.
If you filter for those two events, when either one occurs, you have low memory of some type. To set up the alert, you'll need to connect your PowerShell script to email you in the event you get those results.
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SQL Server Execution Plans
SQL Server Query Performance Tuning