The solution for that seems to be a UPS. I have a BTB alarm and have been perusing NBN plans and so far have yet to find one that openly admits to support it excepting tacitly by adding one’s own UPS to the NBN and ISP equipment.
I suspect the “retail telco ISPs” are not interested in having liability if the systems fail a medical emergency or alarm regardless of whether it is them or the NBN part of the equation.
