Hello Arjan!
You should be able to use object event handling to get your desired result, even on custom objects. You can check out the documentation on this here:
docs.kentico.com/display/K81/Handling+object+events
if you are using portal engine at all you can use this, which is built into kentico for allowing users to subscribe to content changes:
docs.kentico.com/display/K81/Allowing+users+to+subscribe+to+content+change+notifications
if you are using 100% aspx templates then you can use global event handlers to accomplish the same thing, it will just be a bit more work.
Hope this helps!