From: baldwin@LAT.COM (Bob Baldwin)
A fellow I know has a central-office alarm in his home. When the alarm goes off, the office calls his house to ask if it was a false alarm. They ask for a password to verify, and no matter what password you give they say "OK, I'll log it as a false alarm." If you gave the wrong password, they call the police and notify them of a crime in progress with hostages.
For many years, I worked for a small company that provided various protective services to government, diplomatic and executive accounts. One of the services was electronic security and direct monitoring of emergency EDCs [electronic digital communicators] and other signalling devices connected to security equipment. At the beginning of my employment, the procedure you mention above was standard throughout the more mainstream electronic security industry. A series of unusually violent robberies changed this in the mid-1980s. The problem with the system is that call-backs on "panic button" or duress code activations make it clear - or at least suggest - that the victims have alerted the authorities. In an increasing number of cases, answering the callback was literally the last thing the victims ever did. In spite of frequent complaints due to false-alarm fines levied by the police and moments of great embarrassment, the common procedure became immediate notification of of the police or "other security," with no callback then or later. All duress codes on our electronic equipment was modified to perform the exact functions as non-duress codes, but activated silent duress alarms. Since that time, most manufacturers and programmers of security devices have taken that approach - identical function, but with silent alarms.