Some kind of audible ALARM is required by the FCC.
This requirment may be fullfilled with:
Bells, wistles, buzzers or pieciolectric sonic alarms.
Speech
I was probably the first broadcaster to develop speech (in 1993) as an alarm media.
(I WAS the first to develope a talking transmitter.)
Computer application:
There are at least three dedicated computers that do nothing except speech: One located in Master Control,
one located at Cohasset, and one located at Tuscan.
MicroSoft TextToSpeech engines.
Huge draw back to this type of synthesis: The computer must be up and running.
... and that has been a problem: Microsoft fails or the Computer fails!