On pressing the button, it immediately triggers a localized alarm, and after a preset amount of time passes, if it has not been cancelled (usually by someone with an authorization key), it automatically forwards an alarm signal to another remote system(s) (often all other alarms in the area, and fire fighters).

Sorry, the reference document below can't actually be downloaded, but you can see from the title, and your own search of this term, that this is what it is.