ISO: Security that works no cell service / not 100% wifi dependent

I just moved to a home in Los Angeles that has no cell service. ADT came in and installed a security system but without service it isn't working. I know Qolsys IQ Wi-Fi 6 is an option but that worries me because it's 100% wifi dependent.

Does anyone have any suggestions for a security system that can rely on Wifi and then a landline as a back up? Happy to pay extra and have it professionally installed but do not would prefer not to rely on Wifi solely.