Yes. Impervious to EMP.
Well, no; although some TEMPEST implementations provide shielding against EMP. TEMPEST stands for Telecommunications Electronics Materials Protected from Emanating Spurious Transmissions. It's all about preventing eavesdropping on leaking electronic emanations.
Just a nit. I wouldn’t think that listening in on telecommunications would be “emanating spurious transmissions”.
EMP would fit better into that description.