He also said that, unlike the human eye, digital cameras can see infrared light. For example, if you press buttons on your TV remote control while pointing it at your digital camera, you can see the light if you're looking through the viewfinder.
If someone is using infrared technology to transmit a stealth audio recording, Porteous said, you could look through your digital camera to see it.
If you're willing to invest a little money, you can find professional-grade, counter-surveillance technology that can help you root out hidden cameras.
Jeffrey Jurist, president of SpyAssociates.com, said one way to detect covert cameras is through a device that reflects a laser off the camera's lens.
The SpyFinder Camera Detector, for example, is a pocket-sized, battery-operated device that sells for $99.50 on SpyAssociates.com.
"It's a pretty easy-to-use gadget," he said. "[It's] looking for a reflection from the iris lens."
Jurist said the device will identify a hidden camera (whether it's on or off) from up to 15 to 20 feet away and within a range of 5 to 10 feet.
For example, if you wanted to scan a hotel room, he said, you would stand in the center of the room and turn around 360 degrees while looking through the viewing port. If a camera had been hidden in the room, you would see a red blinking light.
For a little more money ($347.50), he said, the Spy Hawk Personal Camera Hunter uses similar technology to identify cameras that are further away and within a wider range.
The Spy Hawk uses two lasers and is the most powerful device of its kind on the market, he said.
For executives and those who worry that someone could be spying on them through other more sophisticated methods, Jurist said he had even more advanced technology.
The Spy Matrix Pro Sweep Bug Detector, for example, can pick up hidden cameras, wire taps, audio recorders and GPS trackers.
The device is just shy of $500, but uses a radio frequency detector to identify the frequency signals being used to transmit audio and video.
It's not for everyone, he cautioned, but added that it covers more ground than most other devices available.
But, ultimately, experts caution that even the most sophisticated technology isn't always enough.
"This is a tough one. It's difficult to protect yourself," Knecht acknowledged, adding that just being aware of your surroundings can help.
If you're at a hotel or out of the house, she said, be aware of people lurking too close or for anything that looks out of the ordinary.
In your day to day life, you might get a sense that someone knows too many details about your private life, she said. If that's the case, you might want to do some checking around your house for cameras or bugs in air vents or fire alarms.
"If people feel that someone might be photographing them, then they need to call the police because it is against the law in most states," Knecht said, although she cautioned that the law varies from state to state.
"This has a really huge impact," she said. "It can really be life-altering for people."