There is often no convenient power on the individual floors so battery powered devices are desirable.
Many systems require wires to be run to each floor and then also to the elevator itself. With a wired system problems with the the wire can develop since the elevator is constantly moving up and down. This is one of the reasons a wireless system is desired.
Wireless Construction Elevator Intercom
These callboxes are left in an auto-turnoff mode so they will not receive any transmissions unless the call button is first pressed to wake them up. So every floor will not hear the communications between the worker and the operator.
What goes in the elevator car depends on whether there is power in there or not. You could just use another callbox but it would have to be taken out of the auto turnoff mode so the batteries would only last a week or so. The callbox would really need to be powered via 12 volts DC.
The third option is a handheld two-way radio. The operator would wear it on his belt and he could use a headset or shoulder lapel microphone to talk to people.
There are two different frequencies this equipment is available in, either MURS or UHF. The MURS equipment does not require an FCC license but antenna height of MURS equipment is not supposed to be over 60 feet. The MURS VHF signals can also travel for many miles, so for buildings that are really high this means you could pick up interference from many miles away. So we recommend you only use this for 6 stories or less.
So in most cases we recommend UHF equipment. It does require hiring a license coordinator to get a 10 year license but in large cities that have a high amount of two-way radio traffic, this will give you a more reliable system.
See more info and pricing here:
UHF Construction Elevator Intercom
MURS Construction Elevator Intercom