susceptibility threshold
1. The amount of undesired signal power required at the input terminals of a receiver to cause barely perceptible interference at the receiver output terminals.
2. In cryptology, the level above which a system has the ability to continue to process critical applications in spite of the fact that it has suffered disruptive or damaging effects (such as contamination with dust, an earthquake, a bomb, etc. ) [INFOSEC, 1994]