Houston people what medical alert devices actually work here?

My aunt’s been living alone in Houston since her husband passed, and she’s had a few health scares recently. I’ve been looking at medical alert devices and Bay Alarm Medical Alert keeps showing up. Sounds good but does anyone know if it really works in Houston? We’ve got spotty reception in some neighborhoods and I don’t want to give her something that won’t work in an emergency. Anyone local using this? Would appreciate any real feedback.