No four digit Oracle version. No platform. Asking for free code.
For most monitoring purposes crontab is an obsolete tool, and poses security risks (hardcoded passwords)
Using dbms_server_alert is possible in any decent version of Oracle.
Senior Oracle DBA
Do not report posts as "abuse" if they are not abusive as this wastes moderators time.
Sybrand was making a valid point that you haven't provided enough details to help, as well as correctly highlighting the potential security issue of using crontab rather than built in functionality of the database (and also hinting that you can use dbms_server_alert).