You can hard reset a G6 if the serial number starts with 80 or 81. if the Firmware version is 1.6.5.25. After this point, there is no way to hard reset any other one of G6 transmitters. But the Sensors you still can!

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How To reset Transmitter

The method is the same for G5 as it is for the G6 with transmitter types (80-81) not for 8G typre on onwards

1. Stop the sensor first
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2. Also did it with a Bluetooth connection to the transmitter and make sure to stop Sensor!

3. To Hard reset transmitter after pressing the top syringe icon and then then select the microphone symbol. Speak into the mic and say (Enable Engineering mode) and then say after pressing the microphone again (Enable Engineering mode) and then say after pressing the mic again ( Hard Reset Transmitter)
   
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4. You might get you have failed message in system status after this so I then did a restart collector and left it for another 15 to 20 mins!

5. Restart your sensor when you have Hard Reset the Transmitter. you can see this in System Status and scrolling to the left. Be patient it can take a while

I managed to get 9 months out of one transmitter without changing the battery and doing a hard reset!

I personally had no issues only a slight delay on fast lows and fast highs apart from that all was ok for me! I'm also not a doctor nor a specialist or Endo Always do a Blood check if you are not sure before you bolus if on a pump Id would have a second thought on doing this at all!