You could use the inherent DBMS's database events. You make an application, preferably set up as a service for constant monitoring, that registers and listens for the event. As soon as the event is raised the service gets the event details (name,text) and acts upon it.

For a good example on it check the event.t source of DBD-IngresII. Might be Ingres specific and not Postgres but it illustrates the point clearly