BT RESPONSE 15 PLUS User Manual page 19

If you encounter a problem and your
Response 15 Plus will not respond to
any button presses, remove the battery
then turn off the power for 10 seconds.
Turning the power back on will reset
your Response 15 Plus to answer-on
mode.
Ensure that your Response 15 Plus is
connected to the mains power before you
insert the back-up battery.
All messages will be lost when resetting
your Response 15 Plus.
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