Battery reporting is notoriously unreliable. You can use a built-in app like Notifier or even Hubitat Safety Monitor (custom rule) to get notifications for battery level, but I wouldn't recommend that for most devices, especially ones where you don't know it's reliable. Monitoring device activity is a fairly reliable method for devices that normally report in on a regular basis (common for motion, contact, etc. sensors that also report temperature or at least check in with battery level or whatnot once in a while and thus generate "activity"), though it does require a bit of knowledge to know what interval without activity is potentially concerning for each device.
There are a few options for this. I wrote one if you are interested:
But keep in mind that Hubitat or HSM is not intended to be used as a security system. There are options for integrating some into Hubitat (e.g., Konnected and similar), but I'm not familiar with any specific options as I do not use it for this purpose. Others may have more ideas.
