Offline mode is entered automatically as soon as either your WIFI internet access disconnects or the ZAP IN servers are offline.

You will know by the small flashing grey icon (box with lightning zap) in the bottom right-hand corner of your Welcome Screen.

Don't worry, visitors can continue to sign in. ZAP IN remembers them, and will automatically synchronize their visitor records with your Dashboard as soon as connectivity is re-established.

Please note: once connectivity is re-established, it will take 4 minutes to run the visitor record synchronization process.

Here's more details on Offline Mode: