TikTok Myth of the Week: The Fingernail Test Shows Whether Hotel Mirrors Are Spying on You

TikTok is full of people “discovering” spy mirrors in their hotel rooms and Airbnbs. Or, more often, they use a normal hotel mirror to demonstrate a trick that supposedly reveals such mirrors. (Phew—this one’s fine! We’re safe!) Unfortunately, these videos rely on a misunderstanding of how mirrors work. Read on and I’ll tell you why these tricks are bullshit, and an easy way of actually telling whether a mirror is two-way. (It doesn’t involve your fingernail.) 

What is a spy mirror, anyway?