In a large Facility it is sometimes not feasible  to run low voltage wiring  from the controller to each horn in this case it is more cost effective to use a combination of wireless remote buzzer stations and wired buzzer stations.
for example  locate a wireless buzzer station at the far end of your facility  to eliminate the point to point  from timer/controller to remote buzzer, then use a combination of wireless remote stations  with wired buzzers the controller/transmitter will power up to 5 additional wired buzzers and control unlimited number of wireless remotes
the wireless remotes can power up to 2 wired buzzers.