Multiple clients can modify the DB and all need to be notified if a DB change occurs.   Where I work, this is implemented with application threads that poll the DB every second or so.  This doesn't strike me as a good way to do it, so I was wondering how do people usually handle this? 
What are some ways people handle DB change notifications?
database
Polling is the most common solution; the other is to have your middle-tier handle the notifications to other services when updates are sent through them. If you have a bunch of clients sharing a database and you can't change them all then for SQL Server you could probably do this with triggers that input messages to the Service Broker and configure other listener actions to notify your clients. I wouldn't start down that road unless you were really confident you need to do that, polling is likely to be better for most projects. You have to consider how this state gets reflected in your clients; most web and client/server technologies are more or less a request/response model so even updating a middle-tier would not matter until your client polled that middle-tier for status.