Allentown, an eastern Pennsylvania city of about 100,000, has managed to keep its neighborhood watch system going since the mid-1970s, with more than 20 individual groups and hundreds of volunteers.

They are not armed, and there has never been an incident, said Assistant Police Chief Joe Hanna.

"We tell them that we are the police, that if you see a crime in progress, get on the phone and call 911. We'll be there promptly, and let us handle the dangerous side of it," Hanna said. "The last thing we want is for them to put themselves in harm's way" or hurt someone else.