CoughDrop can function whether or not you are connected to the Internet. Not all functionality is available when you are offline, but you can still have a fully-functioning communication device when disconnected from the Internet. To do this CoughDrop syncs your vocabulary set to your local device for offline use. Syncing will happen occasionally in the background as well.
Wait until sync is finished
Once the syncing process has finished the button will say "Sync Done!" and your boards can now be used offline. You can also edit and create communication boards while offline, and changes you make will be persisted to the CoughDrop system the next time you re-sync.