It’s a familiar scene from every police procedural: In one brightly lit room, a perp is being questioned. In an adjacent room ...

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.

One classic set you’ll see in most vintage mystery movies is an interrogation room with a “two-way” mirror in one wall. This cool gadget lets the witnesses see the suspects from another room while the ...