For general information on alerts check FAQ note 1330726 (CRM-IC-ALT).
With business function CRM_IC_CEBP, user-triggered alerts can be used if real-time events are not necessary, e.g. if you do not use telephony or ICI mails. KBA 1822577 shows how to create a user-triggered alert, which works without polling.
Starting with CRM 7.0 EHP3, SP3, you can use ABAP Push Channel instead of Polling.
As prerequisite you need a Web browser that supports WebSockets (e.g. IE10). If temporary network connection problems occur, or if launched Web browser does not support WebSockets, the system launches the classic polling mechanism instead. See KBA 1822577 and SCN blogs Replace
polling in CRM Interaction Center by ABAP Push Channel and ABAP
Channels Part 1: WebSocket Communication Using ABAP Push Channels
How to use themes to highlight important alerts with different colors and icons is explained here.