These are devices based on thermal measurement theory, so these devices bkais thermal differences between objects.
According to the speech resource that gold with high heat conductivity, heat stores longer than the remaining objects and even other metals, gold receives heat by day and when evening fade the heat from other objects, gold retains much of this heat.
II caves, caves are cooler areas on Earth where they contain air confined attracts moisture and not intended cave exclusively, but each space is underground.
The device, measuring differences in temperature (increased heat = having gone)
Low temperature = a cave or a vacuum.
Where the device measuring temperatures ranging-30-900 degrees Celsius.
Searching at night and winter are the best times for underground objects got rid of temperature in General