get oracle watchdog

Hi, I like some help, to improve a watchdog on oracle database.
The server daemon could be still running even if the database down. and send a common message like "FAIL on DATABASE"
i know, is just set a cron script or something to monitor that, but i cant.
If some one can tell me with part of source to star reading i appreciate.
tanks.
any explanation about what file.c code is possible to enable this feature. thanks again