Sena Bluetooth SM10 v1.1 User's Guide - Manual (Page 18)

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6.6 Fault Reset
If the SM10 is not working properly or is in a faulty status for any
reason, you may reset by pushing the small reset button at the
back of the SM10 Main Unit. By using a paper clip or a pencil
tip, lightly press and hold the reset button for 1 second. The
SM10 will be switched off and automatically switched on again.
Turn the SM10 back on to use it. However, this will not restore
the SM10 to factory default settings.