The devices requires wifi to connect to cloud based servers that contain the settings and set schedules. Should you only lose connection to the Internet, majority of devices such as thermostats, cameras, smoke detectors will still function, even when your Internet service goes down. The only exception is the function that allows you to remotely control the devices. Once the Internet connection is restored your devices will reconnect automatically to your smartphone.
In the case of door locks, these operate using batteries as a power source which enables you to always access the lock manually or through your smartphone.