From the 2007 elevator code:
2.27.1 Car Emergency Signaling Devices
2.27.1.1 Emergency Communications
2.27.1.1.1 A two-way communications means between the car and a location staffed by authorized personnel shall be provided.
2.27.1.1.2 When the two-way communicationslocation is not staffed 24 h a day, by authorized personnel who can take appropriate action, the means of two-way communications shall automatically be directed within30 s to an additional on- or off-site location, staffed by authorized personnel, where an appropriate response can be taken.
2.27.1.1.3 The two-way communication means within the car shall comply with the following requirements:
(a) In jurisdictions enforcing NBCC, Appendix E of CSA B44, or in jurisdictions not enforcing NBCC, ICC/ ANSI A117.1.
(b) A push button to actuate the two-way communication means shall be provided in or adjacent to a car operating panel. The push button shall be visible and permanently identified as "HELP." The identification shall be on or adjacent to the "HELP" button. When the push button is actuated, the emergency two-way communication means shall initiate a call for help and establish two-way communications.
© A visual indication on the same panel as the "HELP" push button shall be provided, that is activated by authorized personnel, to acknowledge that two-way communications link has been established. The visual indication shall be extinguished when the two-way communication link is terminated.
(d) The two-way communication means shall provide on demand to authorized personnel, information that identifies the building location and elevator number and that assistance is required.
(e) After the call acknowledgement signals are sent [2.27.1.1.3©], the two-way voice communications shall be available between the car and authorized personnel.
(f) The two-way communications, once established, shall be disconnected only when authorized personnel outside the car terminate the call.
(g) The two-way communication means shall not use a handset in the car.
(h) The two-way communications shall not be transmitted to an automated answering system. The call for help shall be answered by authorized personnel.
(i) Operating instructions shall be incorporated with or adjacent to the "HELP" button.
2.27.1.1.4 Where the elevator rise is 18 m (60 ft) or more, a two-way voice communication means within the building accessible to emergency personnel shall be provided and comply with the following requirements:
(a) The means shall enable emergency personnel within the building to establish two-way voice communications to each car individually. Two-way voice communication shall be established without any intentional delay and shall not require intervention by a person within the cat The means shall override communications to outside of the building.
(b) Two-way voice communications, once established, shall be disconnected only when emergency personnel outside the car terminates the call.
© Once the two-way voice communication has been established, the visual indication [see 2.27.1.1.3©] within the car shall illuminate. The visual indication shall be extinguished when the two-way communication is terminated.
(d) Operating instructions shall be incorporated with or adjacent to the two-way voice communication outside the car. Instructions shall conform to 2.27.7.3.