Free Drive Space and SQL Server Agent Alerts
This is an OS information. I don't think there will be an Alert in SQL that will track the remaining space on the drives.
Pretty much all of the monitoring products monitor this and can send you alerts when you reach a specific threashold for disk space.
If you do not have any monitoring tool, then I think that a SQL job that check the free space and send an email seems like a good option.
Here's a script I use to see how much space available there is on the drive where I have a database file (it doesn't work for drive that doesn't host any database file)
SELECT Drive,PercentFree FROM (SELECT  VS.volume_mount_point AS Drive, 
 CONVERT(DEC(4,2),CONVERT(DEC(18,0),VS.available_bytes)*100.00/VS.total_bytes) AS PercentFree 
,ROW_NUMBER() OVER(PARTITION BY VS.volume_mount_point ORDER BY MF.database_id,MF.[file_id]) RN
FROM sys.master_files MF CROSS APPLY sys.dm_os_volume_stats(MF.database_id, MF.[file_id]) VS) as SP WHERE RN=1 ORDER BY SP.Drive