Alerting services can provide a valuable support for information seeking in Digital Libraries (DL). Several systems have been proposed. Most of them have serious drawbacks, such as limited expressiveness, limited coverage, and poor support of federated and distributed collections. In this paper, we present the detailed design and implementation for a comprehensive alerting service for digital libraries. We demonstrate typical user interactions with the system. Our alerting service is open to other event sources, supports a rich variety of event types, and works on distributed as well as on federated DL collections.