Of course the moment I ask for help I figure it out.
Set Error Capture [On]
Go to layout [Assets(Assets)]
enter find mode
insert from device [Assets::Barcode;Type: Bar Code; Camera: Back; Resolution: Full]
show all records
Show Custom Dialog Box
You've posted a Filemaker Go question in the FM Pro forum. That's really no big deal, but thought you should know that there's a section intended for FM GO.
In this case, the question is answered the same for FM GO and FM Pro.
If you add this script step:
Set ErrorCapture [on]
before the perform find step, you will not get the "no records found dialog interrupting your script when no matching record is found.
You can then use:
If [ Not Get ( FoundCount ) ]
To detect the case when no record matching the inserted bar code was found.
For more examples of scripted finds that you might find useful, see: Scripted Find Examples