Microwave ovens most definitely function as faraday cages, however they are specifically designed to attenuate 2.4GHz signals. Anything higher or lower which is

Microwave ovens most definitely function as faraday cages, however they are specifically designed to attenuate 2.4GHz signals. Anything higher or lower which isn't a harmonic (integer multiple) of 2.4GHz is going to experience much less attenuation.