The first hack everyone does to the Spy Trakr is to install a headphone jack. I jumped on the band wagon. My biggest issue was the mic-speaker feedback when I had the Spy Trakr next to the remote; LOUD!
So I opted for headphone jack AND a volume knob.
I carved out a slot in the right grip with a soldering iron (it is a sin, I know) for the jack (ebay 5-pin) and a small wheel potentiometer (Radio Shack 271-001). This 5-pin jacks automatically switch from speaker to headphone when you plug it in.
This is a crude wiring diagram. It is sad how long it took me to figure it out.
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This is a shot of the holes and where the stuff fits in the remote.
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The components assembled and awaiting final gluing.
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The final installed setup.
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The speaker shuts off when the headphones are installed.
Speaker: the wheel controls the speaker from NORMAL to mute. Not a lot of fine control.
Headphones: the wheel controls the headphones from REALLY LOUD to NORMAL.
Overall, I am happy with the results.