Different components have different ratings. The ATmega328 may work down to -55C (does it?) but the oscillator probably won’t, and neither may some of the other devices. The FT232 should be good to -40C as should the voltage regulator. Yeah, I’d say the oscillator is the big question mark.
if it’s not exposed I bet it wouldn’t be an issue. If you think about something like my garage door keypad, it might not work at -37 but I bet it would be the battery that let it down. It’s only protection is its own cover and a little bit of wind shadow.
I ran a little test in my freezer running the blinking LED example sketch on an Arduino NG. It’s nestled right between some steak and the ice cube tray.
-18C and it seems to run fine. I can’t vouch for accurate timing, but it seems to blink on time. I’ll leave it in there for a week and see what happens. Shouldn’t affect the steak flavour, either.
Yep had mine in the freezer for an hour at -18°degC. Powered by Li-Ion battery, continued to log the GPS position of my fridge (antenna hanging outside the door) and internal freezer temperature to an SD card.
Remember there will be condensation if you are moving from cold to warm temperatures quickly.