Right now, only the official smartlighting feature and a few bits of smart home monitor can run locally, and then only if they are limited to devices using device type handlers which can run locally. Routines cannot run locally, you cannot arm/disarm smart home monitor locally, and you can’t use the app on the phone locally even if your phone is on the same LAN as your hub.
There’s no official list of the handlers, but there is a community thread of handlers that have been confirmed to run locally. There are several sensors there:
Here is a list of the Device Handlers that are confirmed working with local processing (I personally tested that these show up in the “LocalDevice List”) as of Dec 8, 2017: Device Type Run Locally Execute Commands Locally Minimum HubCore Version Aeon Home Energy Meter TRUE FALSE n/a Aeon Illuminator Module TRUE FALSE n/a Aeon Key Fob TRUE FALSE n/a Aeon Minimote TRUE FALSE n/a Aeon Multisensor TRUE FALSE n/a Aeon Multisensor Gen5 TRUE FALSE n/a Aeon Outlet TRUE FALSE n/a Aeon Siren TRUE FALSE n/a Arrival Sensor TRUE FALSE n/a CentraLite Thermostat TRUE FALSE n/a Dimmer Switch TRUE FALSE n/a Fortrezz Water Valve TRUE FALSE n/a GE Link Bulb …