In one of the applications I support we use Big Brother monitoring tool to control status of a lot of things, including an Oracle db. It's freeware (
http://bb4.com/).
Basically, it is a collection of scripts that run periodically and then report their respective status on a web page (potentially sending an email alert, too), where you can drill down and view status change history. For Oracle I have a java app. "plug-in" because I need some tricky reporting but if you only want a "ping" to the database then a small script querying sysibm.sysdummy1 would be sufficient.
There are many plug-ins available contributed by the people who use it.