Hi,
I also own a Spectra 1738. I want to interfacing with it using arduino.
The data here is very usefull for my project: Monitoring my house 
For now, i have temperature, humidity, sound detection, flood warning, etc... But nothing from my alarm system... Everything can be accessed by web.
My biggest problem is that I cant find which pin is what on the serial ouput port? can you tell me which pin is Tx, gnd and VCC?
I tried to find the ground of the board but couldn't find it... I'm pretty new to electronic and without a known ground, it's hard to find the pin used for ground.