Using a QR code for a device allow you to identify and open the device and activities. It works very similar to NFC tags, however a QR code cannot be used to start and stop tasks, due to the possibility to duplicate.
To create a QR in Alldevice you can open a device and click the "Share" and "Generate QR"
Example
This will open (possibly in a new tab) the QR code and you have options to print or copy.
Scanning the QR with a phone will open the Mobile version of Alldevice and open the device linked to the QR code,