LAS VEGAS (KLAS) Mary Ferguson, a longtime advocate against smoking, was taken aback when she discovered a $419 smoking fee on her hotel bill, sparking concerns about the reliability of smoking detection systems used in Las Vegas hotels.

Ferguson, who visits Las Vegas monthly with her husband, chose to stay at the Rio Las Vegas in July. The attraction was the hotel’s recent renovations and a special deal she received.

“Everything was great until we checked out,” Ferguson recalled. “That’s when we encountered this issue.”

Upon checkout, Ferguson was shocked to find a $419 charge for smoking on her bill.

“Neither I nor my husband smoke,” Ferguson emphasized. “We have never smoked. In fact, I’ve spent nearly 20 years as a health educator working on tobacco cessation.”

Ferguson said she worked for a health system, training nurses and teaching them why tobacco is dangerous to their health. The night connected to the violation, she and her husband retreated to their room early to avoid any smoke on the property, which offers all non-smoking rooms.

“We just don’t like to be around it,” she said. “So here it was 9:30 in the evening on a Saturday, and we’re back in our room trying to stay away from it, only to be accused of smoking in the room.”

A smoking violation report Ferguson provided shows the smoke was reportedly so bad in the hotel room – the smoke index, which is normally between zero and 10, hit a whopping 100. The air quality figure came in as “hazardous,” the highest on the scale in the report.

“They’re telling you that you survived, basically a fatal smoking event,” 8 News Now Investigator David Charns of Nexstar’s KLAS said.

“Right,” Ferguson responded. “We fell asleep shortly thereafter. We went to bed afterward. I had no idea that we had this, you know, toxicity in the room whatsoever. There was no one knocking at our door. No alarm went off. Nothing. Like I said, the only indication we had that this was an issue was upon checkout, and the fee was charged.”

“It’s your word against the hotels, and you have to you will have at least some ammunition before you get into that room,” CBS News Travel Editor Peter Greenberg said.

Greenberg advises travelers to document as much as they can during their stay to prevent any incidental charges. This includes photographing any damage in the room and the minibar.

“What’s your advice for travelers who have a great time here in Vegas and then get one of these fees and just don’t have the proof to say, ‘Yeah, I actually wasn’t smoking?’” Charns asked.

“One is your own medical history. You basically prove you’re not a smoker,” Greenberg said. “Number two, you apparently paid for the bill with your credit card. You can dispute the bill on your credit card because you were charged for something you didn’t contract for.”

Oftentimes, credit card companies will waive the charge because fighting it is more costly, he said.

Complaints with the Better Business Bureau show 28 entries referencing smoking at the Rio since March. Many of their authors also write that they do not smoke. Hotel leadership responded to some of the complaints, adding that the violations could be “one-offs” or “isolated.”

“I don’t have a problem paying for something that was ours. It was not,” Ferguson said.

“All guest rooms at Rio Las Vegas are non-smoking,” a spokesperson for the property said Thursday. “We utilize air quality monitoring technology to enforce this policy, which is consistent with other properties in and around the Strip. Each violation is reviewed thoroughly to ensure fairness, and we remain committed to maintaining a safe and comfortable environment for all guests.”

Amid the 8 News Now Investigators’ questioning, the Rio waived the fee, Ferguson said.