How to detect a two-way mirror

You’ve just checked into your hotel or Airbnb. It’s been a long day and you can’t wait to tear your clothes off and jump into the shower to freshen up.

But before you do, take a closer look at that mirror hanging on the wall. Is it just a mirror, or could someone also be using it to spy on you?

If it’s a standard piece of glass covered with a mirror film, it will be really obvious because you’ll be able to see bubbles and scratches on the film. That means it’s a transparent mirror that could be used to view you and your room. No obvious film? Here are three sure-fire ways to spot a two-way mirror.

1. The fingernail test

Hold your fingernail against the surface of the mirror. If you can see a gap between your finger and its reflection, it’s a normal mirror. But if your finger touches its reflection with no gap, it’s more than likely a two-way mirror. A word of caution – although most two-way mirrors can’t pass the fingernail test, some can. So to be 100% sure…

2. Knock, knock. Who’s there?

Knock on the mirror. Can you hear a bit of an echo? Then there’s probably a hollow space behind the mirror, which could conceal a hidden room or camera. A normal mirror will produce a solid, dull sound because it’s being properly supported by the wall behind it. But the best way to tell if it’s a two-way mirror?

3. Lights, camera, action

Get your smartphone out and switch on the flashlight. Draw the curtains and switch off the lights. Now put your phone flat against the mirror. If you can see light leaking through to the other side of the mirror there’s an empty room behind it. Get the hell out of there and demand an immediate refund! If there’s no sign of light passing through, it’s definitely a normal mirror. You’re good to go.