This is my RF detector, which I paid $79 for on Amazon and can pick up radio signals. Todd Haselton | CNBC

Numerous reports over the past several years have suggested Airbnb hosts are using cameras to spy on guests. Some hosts might have a relatively innocuous Nest Cam outside to keep track of who comes and goes, but others can be used to watch you while you roam about the house. There have even been reports of cameras in hotel rooms.

Smile! Todd Haselton | CNBC

Airbnb's terms says it requires "hosts to disclose all security cameras and other recording devices in their listings, and we prohibit any security cameras and other recording devices that are in or that observe the interior of certain private spaces (such as bedrooms and bathrooms), regardless of whether they've been disclosed." Cameras have to be disclosed even if they're unplugged, and any disclosures following a booking give a host the option to "cancel the reservation and receive a refund," though that refund may still require a cancellation penalty.

It's thin and well built. Todd Haselton | CNBC

If you're worried about this, there's a $70 gadget you can buy on Amazon that will let you do a quick sweep of any room for cameras. While it's not as advanced at detecting cameras that are meant to hide wireless signals -- those professional tools are much more expensive -- this RF detector can pick up most cameras someone would buy and that are physically hidden, whether they're in a plant, in disguise or out in the open. I looked for it after The New York Times reported that a Chinese woman was caught with a hidden camera detector at President Trump's Mar-a-Lago resort and decided to give a cheap one a try. It's great. Here's how to use it. Don't worry, it's very simple.

The hidden camera detector

The indicator lights tell you if there's a wireless signal and an alarm will sound from the built-in speaker. Todd Haselton | CNBC

This is the RF detector I bought from Amazon for $70, from a company called Eilimy. It finds and alerts you to radio signals from devices that might be connected to the internet. That includes things like cameras that are in places they shouldn't be. It's tiny, though a bit too big for a pocket given the antenna (which can unscrew off of the top.) There's a bar with indicator lights that are green when it doesn't spot anything, but turn to red when it finds a signal. A knob allows you to turn up the power, so it can spot things that might be further away. Doing this, however, means it'll go bonkers with regular things, like Wi-Fi networks, so you don't want to turn it up too much. I'll talk about that in the next step.

The device is simple in its execution, but works. Todd Haselton | CNBC

There are dozens of these sorts of RF detectors available on Amazon. I can't vouch for all of them, but this one worked well for me. There are more advanced devices you can buy with all sorts of graphs that show you the type of signal you're getting. But this is simple and cheap and just basically says "yes there's a wireless signal around," or "no there isn't."

A couple of spy cameras I tested

A couple of spy cameras I bought on Amazon. One looks like a USB charger. The other is a tiny camera at the top of a ribbon attached to a battery pack and antenna. Todd Haselon | CNBC

I bought a couple of cheap and easily hidden cameras on Amazon to see if my detector was able to spot them. It worked on each one. Both of the cameras use wireless networks to send a live stream or recorded video back to the host's phone.

This ribbon camera can hide almost anywhere. Todd Haselon | CNBC

One is a very tiny camera on the top of a ribbon that's connected to a battery and which can easily be hidden inside of a plant or over the top of another electronic device, or taped to the wall. This looks like a normal bookshelf, for example:

You can barely see the spy camera hidden against the Robert Frost book here, along the edge of the picture frame. Todd Haselon | CNBC

But I've hidden the ribbon camera right here:

And here I'm implanting it in a plant:

I'm hiding the ribbon camera in a house plant. Todd Haselon | CNBC

The other one I tested is designed to look and function like a normal gadget charger.

It looks like a normal USB charger. See the camera? Todd Haselon | CNBC

It looks like any other USB plug but there's a camera hidden in it. You wouldn't look twice at it, and the camera can only be spotted if you look very closely. Since most people don't expect chargers to spy on them, they probably don't even look for something like this.

If you look close, you can see the camera. But who inspects chargers? Todd Haselon | CNBC

The RF detector can pick these up, even if your eyes can't.

How to spot a hidden camera

My $79 RF detector, which can alert you of wireless signals coming from hidden cameras. Right now it doesn't see anything. Todd Haselton | CNBC

The trick with setting up an RF detector is to turn up the power just enough so that it can pick up a nearby wireless signal, but not so much that it starts beeping and alerting you about gadgets you already know about, like your cell phone or a Wi-Fi hotspot. To set it properly, tap the silver power button to turn it on and twist the knob on top a tad. Then hold it close to something like your phone so that it buzzes when it's nearby, but quiet when you pull it away.

My $79 RF detector, which can alert you of wireless signals coming from hidden cameras. You adjust the power using this nob on top. Todd Haselton | CNBC

Now it's time to begin your sweep. Some pointers: Think about where you'd hide a camera if you wanted to watch someone. Maybe you'd point it at a bed, a conference table, a desk in a hotel room or a bathroom. Then look around the areas that would allow someone to aim a camera at that specific spot, and search there. Typically, this means doing a sweep around the edges of a room, and examining things that seem innocuous like furniture, plants, books and even chargers.

Wait for the lights to go nuts near a wireless device, like a connected spy camera. Todd Haselton | CNBC

You want to get the radio frequency (RF) detector as close to a suspected camera location as you can. And don't worry if it goes off near normal things that have wireless signals, that's what it's supposed to do -- pick up frequencies. These products can include a smart TV with Wi-Fi, a connected cable box, an Amazon Echo or connected home device. The idea is to try to find a signal coming from somewhere or something that shouldn't have a connection, like a plant, a charger or a piece of furniture.

The indicator lights turn red and a really loud and annoying beep will blast from the RF detector if it finds a wireless signal. Todd Haselton | CNBC

You want to bring the RF detector's antenna near these objects. If it picks up a signal, it'll make a really loud and annoying beeping sound and the indicator lights will flash yellow or red. Again, this doesn't mean it found a camera, but it does mean it found something with a wireless signal. So if you stumble on a potted plant that's setting off the RF detector, take a closer look. It's possible there's a connected camera there. Note that the device will only pick up devices when they're broadcasting over a wireless connection. So, if someone has a hidden camera that doesn't broadcast, but only stores the video for viewing later, then this won't detect it. But, in today's connected world, most people want a live feed and are probably using a camera connected to the internet. Here are a couple of examples.

Hidden camera?

I hid a camera in this plant. It's hard to see from far away. Todd Haselton | CNBC

Potted, but spotted:

The RF detector makes a loud beeping noise and the indicator bars turn red when it finds a wireless signal. Todd Haselton | CNBC

Hidden camera?

There's a camera hidden right on the face of this charger that I bought on Amazon. Todd Haselton | CNBC

Found you.

The RF detector spots the signals coming from the camera, giving me an indication something fishy is . going on. Todd Haselton | CNBC

What to do if you find a hidden camera