Are you still using the 9v wall wart from Sparkfun? It is regulated (switching) to 9V output as long as the input is greater than 100vac. Is it possible the refrigerator and/or some other device (A/C?) is causing the line voltage to sag below 100v long enough to shut down the regulator momentarily?
An o-scope would be really helpful at this point.
add: I noticed you even moved the power to your room where it worked, and it fails in the garage. Just out of curiosity, do you have a memory card in the microSD slot? You had mentioned in your code posted that you had planned to use the SD card to log stuff.
Your code appears to have no timeout function if the connection breaks (not closed). That could cause it to fail.