On the 11th of January 1805 Admiral Missiessy left Rochefort with 5 sail of the line, undetected by the British forces on the coast.
You may temporarily find a safe distance to travel undetected, but eventually you will be found and dealt with.
Now, whether a real, though undetected, change occurs is a question to be determined from case to case; it is certain, however, that a substance like aragonite (a mineral form of calcium carbonate) has sensibly persisted in geological periods, though the polymorphous calcite is the more stable form.
It is probable that the whole phenomenon of isomerism is due to the possibility that compounds or systems which in reality are unstable yet persist, or so slowly change that practically one can speak of their stability; for instance, such systems as explosives and a mixture of hydrogen and oxygen, where the stable form is water, and in which, according to some, a slow but until now undetected change takes place even at ordinary temperatures.
How would you define undetected? Add your definition here.