Hi Debbie
It is errattic, usually after midnight Friday / Saturdays and Sundays, i.e. weekends. It is sometimes twice a month then doesn't happen for a few months.
As I said sometimes after the bleeping of the alarm wakes us up, reset alarm, go back to sleep then it does it again a couple of hours later waking us up again. I cannot reset the alarm until the phone line is reconnected, The warning Bleeps happen when alarm is unset.
The alarm is monitored and usually not set when we are in, although the panic buttons are constantly active, the alarm company says the warning tone cannot be disabled as it is a safety alert to warn that intruders may be attempting to tamper with alarm.