Divyanshu, thank you for your answer.
I had a similar idea to check the DB log file for failed log backups. The problem is that when I opened the log file from the dbacockpit, I found no errors/warnings for the days that our log backups did not run or failed. Here is a small part of that log to show you what I mean. In this example, the log backup was not running from 25th of July until the 28th of July when we fixed the log backups again, after receiving a disk space warning (log disk drive was almost full):
The last successful log backup is mentioned in the log: "20140724091524 Backup Log was backed up"
Then as the days go by, there is no backup failure entries whatsoever to look for them in the log:
20140725000023 spid18s This instance of SQL Server has been using a process ID of 1304 since 5/27/2014 11:50:00 PM (local) 5/28/2014 6:50:00
20140725000023 spid18s AM (UTC). This is an informational message only; no user action is required.
20140726000020 spid21s This instance of SQL Server has been using a process ID of 1304 since 5/27/2014 11:50:00 PM (local) 5/28/2014 6:50:00
20140726000020 spid21s AM (UTC). This is an informational message only; no user action is required.
20140727000023 spid22s This instance of SQL Server has been using a process ID of 1304 since 5/27/2014 11:50:00 PM (local) 5/28/2014 6:50:00
20140727000023 spid22s AM (UTC). This is an informational message only; no user action is required.
20140728000022 spid17s This instance of SQL Server has been using a process ID of 1304 since 5/27/2014 11:50:00 PM (local) 5/28/2014 6:50:00
20140728000022 spid17s AM (UTC). This is an informational message only; no user action is required.
Until finally on the 28th we restored the log backup functionality:
20140728042814 Backup Log was backed up. Database: XXX, creation date(time): 2010/12/22(16:45:29)
So, I find it difficult to deduce an appropriate string to look for in the log, in order to generate an alert when my log backups are not working.
Any suggestions? Am I looking at the wrong place perhaps?