How cold?

[jBay]

I’d like to capture how cold it really was when I see out overnight.
The temperature gauge on my watch, shows me the warmth inside my sleeping bag.

Any one got a small and simple solution, that works?

[Zippy]

small USB data logger? They don't cost a lot either...

Or even, just a backup battery on your Garmin if it has a thermometer on it.

Cheap weather station with max/min will also do the trick.

[whitestone]

If you've an ANT+ compatible Garmin then they do a temperature sensor called Tempe. Pair it up then just stick it in a bag within a few feet of the Garmin and they'll chat merrily away.

[thenorthwind]

Take your watch off and put it outside your sleeping bag?

[voodoo_simon]

Really simple?

Leave the watch outside...

[Alpinum]

Take your watch off and put it outside your sleeping bag?

Same here. And there's also the GPS unit (given a temp. compensated Barometer is included).

[Blair512]

Chuck one of these in your bag and leave it out overnight?

https://www.amazon.co.uk/Silverline-Mea ... ref=plSrch