If it ever happens that you've misplaced your barcode scanner, for example in the warehouse, you can quickly find it again using Apple's Find My iPhone feature.
To do this, log in at https://www.icloud.com/find/ with the Apple ID that you're also signed in with on the device.
You'll now see the approximate location of all devices with this Apple ID on a map.
Click on the corresponding point on the map, or select the device you're looking for at the top via All Devices.
A window will now open in the top left. Click Play Sound there so that a beep is played on the device you're looking for. Now follow the sound to find your scanner.