Duress code

Typically, the warning is given via some innocuous signal embedded in normal communication, such as a code-word or phrase spoken during conversation to alert other personnel.

Entering the code when under duress from an assailant can trigger a silent alarm, alerting police or security personnel in a covert manner.

[2] They noted duress PINs have never been actually implemented in any ATM, and conclude that the costs of deployment outweighs the likelihood they will actually deter criminal activity.

Ideally, the use of a duress code has been confirmed before the current situation, so the family member or friend has verifiable evidence that something is wrong, and when the authorities are notified aren't just limited to speculation.

There are technical issues that could pose problems, such as a delay in notification, cellular network availability, and the fact that a location is not disclosed, only the activity.

Typically, this meant using escape and evasion procedures, before the captured agent was tortured by the Gestapo and forced to give incriminating information such as names and addresses.

In a major Cold War incident in 1968, the US Navy ship USS Pueblo was attacked and captured by North Korean forces, and the crew was abused and tortured during the subsequent 11 months.

[10] US Navy Admiral Jeremiah Denton became famous for blinking out the word "TORTURE" in Morse code during a propaganda television broadcast when he was captured by North Vietnamese forces during the Vietnam War.