Despite the temptation to argue with Geoff just to see where it goes I have to say I agree.
We carry hand held thermal imaging cameras on our fire apparatus that are intended to see where hot spots are in side walls, etc.
When we get calls for missing people we use them in the woods. A decent TIC can show you a wide range of temperatures.
You are really just looking for areas that are warmer than the surroundings and even a few degrees will show up reasonably well.
The leading company in thermal imaging is FLIR. They make cameras for the fire depts, industrial and military ones. They even have one that
will plug into an Android or iOS phone.