/etc/sane.d/sm3840.conf is in libsane 1.0.23-3ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | # usb vendor product
# Microtek ScanMaker 3840 ID
usb 0x05da 0x30d4
# Microtek ScanMaker 4800 ID
usb 0x05da 0x30cf
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