I have a process that reads raw data and writes this to a database every few seconds.
What is the best way to tell if the database has been written to? I know that Oracle and MS-SQL can use triggers or something to communicate with other services, but I was hoping there would be a technique that would work with more types of SQL databases (SQL lite, MySQL, PostGRES).
Your question is lacking specifics needed for a good answer but I'll give it a try. Triggers are good for targeting tables but if you are interested in system-wide writes then you'll need a better method that is easier to maintain. For system-wide writes I'd investigate methods that detect changes in the transaction log. Unfortunately, each vendor implements this part differently, so one method that works for all vendors is not likely. That is, a method that works within the database server is unlikely. But there may be more elegant ways outside of the server at the OS level. For instance, if the transaction log is a file on disk then a simple script of some sort that detects changes in the file would indicate the DB was written to.
Keep in mind you have asked only to detect a db write. If you need to know what type of write it was then you'll need to get into the transaction log to see what is there. And that will definitely be vendor specific.