You could look at Postgres, which has NOTIFY. There also are many, many other methods of doing inter-process communication (IPC). Maybe using the filesystem and inotify works on your OS, or simply writing to a pipe. Using some kind of shared memory as a blackboard is also a good approach if all you care about is whether there are new events.

You could also look at adding a message queue (server) to your setup. This brings another server into your setup. You could also use long polling HTTP ("REST") requests to notify you of a change.

In any case, you will be looking at adding a message queue to your setup, or at least a notification queue. This will bring you additional headaches as you will need to plan on whether receiving a message and acting on it is idempotent or not. It will bring you greater flexibility because you can easily add more subscribers to your infrastructure that way.