Don't underestimate the dynamic range of a modern wifi transceiver. It is transmitting at ~20dBm and will receive down to at least -80dBm. You need to achieve >

Don't underestimate the dynamic range of a modern wifi transceiver. It is transmitting at ~20dBm and will receive down to at least -80dBm. You need to achieve >100dB attenuation, well beyond what a microwave oven provides. Even a solid metal box with a few small holes will struggle.