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 displayed on a map.
Click on the corresponding point on the map or select the device you're looking for from All Devices at the top.
A window will now open in the top left. Click on Play Sound there, so a beeping sound plays on the device you're looking for. Now follow the sound to find your scanner.