Does the Datacolor LightColor Meter work when no cellphone service and/or WiFi service is available?

Yes, once the Datacolor LightColor Meter app and the device has set up once , Datacolor LightColor Meter app will work with your mobile device when no cellphone service or WiFi is available.
The connection between the Datacolor LightColor Meter app and the Datacolor LightColor Meter device is a Bluetooth Low Energy (BLE) connection.

Do you need additional help?

Please submit a support request (ticket) here.