Do those wearable medical alerts work near the beach or is that sketchy?

So my grandma lives a couple blocks off the beach in Hollywood and we’ve been thinking about getting her a medical alert thing. She had a little fainting thing last week and thankfully someone was there, but she was outside walking near Tyler St and it got me nervous. I’ve heard that some of those devices rely on signal or GPS or something, and not all of them work great everywhere. Bay Alarm Medical Alert came up a lot when I was googling. But I’m not sure how well it actually works in Hollywood. She’s out walking a lot and we don’t want to waste money on something that won’t even connect when she needs it. Anybody local using one of these things and know how it handles around here?