Some airliners are equipped with those kind of systems (included as a subsystem). They can be activated in the cabin or cockpit with a certain knob and initiates a automatic evacuation/emergency procedure, depending on the airlines preferences (also possible, that the system is set permanent inop an the procedures are performed by the cabin attendants only).
Overhead-panel of an A340, left side in the middle area:
Photos: Airbus A340-541 Aircraft Pictures | Airliners.net