Smartthings does not detect device disconnection.
The door lock (KwikSet 910 Z-Wave) is normally connected to the hub (V2), and its operation and status updates are good. I accidentally removed the battery from the door lock, but the app does not detect the offline status of the door after a day. Of course, the battery was removed all day.
Device Health is On. What is the problem?
Are you using a custom device handler for it?
Device health can take upto a day or more to detect if devices are offline. This is because some devices are sleepy devices and can take upto 48 hours before they “wake” up. I believe ST had made adjustments to their device health to avoid a lot of false positives they were getting from sleepy devices.
Device health isn’t a real-time system but rather a slow end state detection mechanism. It’s designed to identify devices who’s battery may have died or lost its connection to the hub (mesh problems / RF interference etc) and can take days to show up.
Plus as @Automated_House said if you’re using a custom DTH ensure that it supports device health.