Airbnbs have changed the way a lot of people travel. Instead of squeezing your entire family into a small hotel room, you can rent an entire house practically anywhere you’d like to stay. If you’re a solo traveler, you can save big by renting a room instead of an entire hotel room that you may not need. It sounds great, but is it safe?

While there are certainly a lot of reputable Airbnb hosts who you can completely trust, it’s a good idea not to assume that your host is up and up. Instead, there is one big precaution you can take to see if you’re being spied on by your host.

A police officer recently shared a video on TikTok that is super helpful when you’re staying at an Airbnb, but it could be used in other circumstances as well. His tip involves an easy trick to find out if the mirror in your Airbnb (or, for that matter, any mirror anywhere) is actually a real mirror or a two-way mirror.

According to the video, all you have to do is touch the glass of the mirror with your finger, and then look closely at the reflection of your finger. If it looks like there is space between your finger and the reflection of your finger “you’re safe.”

Watch this police officer’s TikTok below.

@b_ry91If there’s a space, you’re in a safe place. 2 way mirrors are easy to install in an Airbnb. Give it a quick check next time.♬ original sound – Sleppy

According to Twowaymirrors.com, if you put your finger on the mirror and the reflection of your finger looks like it’s touching your finger without any space in between, the mirror is a two-way mirror.

If you don’t trust this finger test, there’s another easy test that you can do with another mirror, such as a makeup mirror from your luggage. Take out the mirror and put it next to the mirror at your Airbnb. Does the tint of both mirrors look the same? If so, you’re good. If the tint of the Airbnb’s mirror is darker, it’s probably a two-way mirror.

Wait, there is an exception. Acrylic two-way mirrors can be installed backwards which makes it look like there is a space between a finger and the finger’s reflection. The tint can also look similar to that of a regular mirror. What do you do in that case? Touch it with your fingernail. It may feel different than a regular mirror.

You can also try knocking on the mirror like you would knock on a door. Does it sound solid, like the mirror is hooked directly to a wall? Then you’re probably good. If it sounds hollow, there could be a room on the other side or a space where a camera is installed behind the mirror. Watch out.