In this paper we demonstrate that complex oscillations precede the fatigue collapse of nano-electromechanical systems. As a prototype of working nano-device, we consider a nanowire-based nanoswitch loaded by a periodic electro-mechanical force. Just before failure, nano-sub-harmonics are abruptly generated in the nano-displacement field. Such a forewarning, found to be larger for smaller systems, could thus be used as a simple binary tool for monitoring the nano-system integrity, atomistic cracks remaining undetectable by current microscopes.