Minimal debugging output is generated by default. You can increase the output in different ways. Easiest is to increase debug level on the fly with the running sensorfwd. Output can be seen with

journalctl -af

Dynamically increase debug level from command line:

devel-su
kill -USR1 \`pgrep sensorfwd\`
twice for highest output level.

For status report:

devel-su
kill -USR2 \`pgrep sensorfwd\`
Static increase debugging level

If running from systemd, edit /lib/systemd/system/sensorfwd.service and change --log-level=warning to --log-level=test or do:

devel-su
sed -i -e 's/--log-level=warning/--log-level=test/' /lib/systemd/system/sensorfwd.service

then run

devel-su
systemctl daemon-reload

Then reboot or

systemctl restart sensorfwd