What type of system is your script running on - *nix, Win32, Win32/Cygwin etc? At the sacrifice of portability, that would tell you if the alarm approach will work on your system.

One thing you could do is try to telnet to the port on the remote machine - you won't get a sensible response, but if you get a connection refused or other error, that means network connectivity or other more fundamental issues are your problem.
e.g. telnet oracle_host 3306
would try to telnet to machine oracle_host on port 3306 (which happens to be the default port for MySql - use the Oracle port number that you have configured!)