The web person for the Seattle PD wrote:
The Seattle Police Department is making it easier than ever before for you to find out about crime happening in your neighborhood. With Tweets by Beat, you can follow or view a Twitter feed of police dispatches in each of Seattle’s 51 police beats, and find out about the flashing lights and sirens on your block.
In order to protect crime victims, officers, and the integrity of investigations, calls will display one hour after a dispatcher sends the call to an officer. The feeds also do not include information about domestic violence calls, sexual assaults, and other certain types of crimes.
http://www.seattle.gov/police/tweets/