Does Heirloom work offline in the field?

For looking at your plan, yes, in the mobile app, so your plan goes where the signal doesn’t. Before you head to a field without signal, open the app’s Settings and tap Download data for offline use.

Offline, you can look but not change: completing a task or recording a harvest needs a connection. Back in signal, Force resync brings the phone up to date.

The web app needs a connection. More on the app in Is there a mobile app for Heirloom?