This is pretty incredible:

Americans most regularly encounter this technology, known as speaker recognition, or speaker identification, when they wake up Amazon’s Alexa or call their bank. But a decade before voice commands like “Hello Siri” and “OK Google” became common household phrases, the NSA was using speaker recognition to monitor terrorists, politicians, drug lords, spies, and even agency employees.

The technology works by analyzing the physical and behavioral features that make each person’s voice distinctive, such as the pitch, shape of the mouth, and length of the larynx. An algorithm then creates a dynamic computer model of the individual’s vocal characteristics. This is what’s popularly referred to as a “voiceprint.” The entire process — capturing a few spoken words, turning those words into a voiceprint, and comparing that representation to other “voiceprints” already stored in the database — can happen almost instantaneously. Although the NSA is known to rely on finger and face prints to identify targets, voiceprints, according to a 2008 agency document, are “where NSA reigns supreme.”

Hmmm….

The voice is a unique and readily accessible biometric: Unlike DNA, it can be collected passively and from a great distance, without a subject’s knowledge or consent. Accuracy varies considerably depending on how closely the conditions of the collected voice match those of previous recordings. But in controlled settings — with low background noise, a familiar acoustic environment, and good signal quality — the technology can use a few spoken sentences to precisely match individuals. And the more samples of a given voice that are fed into the computer’s model, the stronger and more “mature” that model becomes.
So yeah, let's put a microphone in every room of our house so that we can tell Alexa to turn off the lights. What could possibly go wrong?

Source: The Intercept