I even believe there is an attack which measures fluctuation in the AC current to the power supply. Might as well add power supply masking via a motor-generator set or inverter/on-line UPS that obfuscates/filters transients from the load to line.
EDIT: link here: https://threatpost.com/blinking-router-leds-leak-data-from-a...
Or using appropiate lenses to "look through" blinds or other materials that have tiny lensing gaps which the typical person regards as not see-through.
It's also relatively easy to defend against as well.
Or van eck phreaking.
Or sell them tattletale electronics, like ethernet or usb cables.
Or rubber hose em.
Or ask scroogle/fecebook.
https://en.wikipedia.org/wiki/Electrical_network_frequency_a...
Not limited to audio forensics as the article mentions.