Continue to join the multi-device beta. Source: Android Central Once you've joined the beta, you can connect a new device to your account by hitting the Link a device button. Before you do so, go to web.whatsapp.com on the target device. Enter your phone's passcode or biometric information and use the QR code reader to scan the QR code from WhatsApp Web on the target device. Your device should now be linked to your account, and you can use WhatsApp on that device even without being connected to your phone. Source: Android Central Can I use my WhatsApp account on more than one phone?