Does your lift intercom meet the EN81-28 criteria? 

Lift intercoms must have additional features with respect to the safety of the passengers using the lift. For example, the intercom should send out its location when someone pushes the alarm button. In case of power failure, the intercom should have an emergency power supply which lasts for more than an hour. Outside of the lift cabin extra intercom modules must be mounted to enable the lift technicians to communicate with the passengers or to send out an alarm themselves.