Drew, to make those sensors work we should illuminate the other side of the shutter, when shutter is open the light illuminates the photodiode (or phototransistor, or photoresistor) and then that sensor allows to pass an electrical current that goes to the audio input. The audio input does not know if the signal comes from a microphone or from a photodiode... so it records just the input voltage in the way it is intended, sadly audio inputs usually have a series capacitor to filter out DC, but anyway it will be possible to see shutter action.
There was some confusion around that, as the device is connected to the audio input some sources were saying that it was a microphone, but at least the devices I see at ebay are all optical...
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