LAS VEGAS (KLAS) — Mary Ferguson, a former anti-smoking advocate who devoted years to battling tobacco use, was taken aback when she discovered a $419 smoking fee on her hotel bill. This incident has sparked concerns about the reliability of smoke detection systems used by Las Vegas hotels.

Ferguson and her husband, who make monthly trips to Las Vegas, decided to stay at the Rio Las Vegas in July. They were attracted by the property’s recent renovations and a compelling offer.

“The trip was going smoothly until we checked out,” Ferguson recounted. “That’s when we encountered this unexpected issue.”

Upon checkout, Ferguson noticed that the hotel had imposed a $419 charge for smoking.

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

During her career, Ferguson trained nurses on the health risks associated with tobacco use. On the night in question, she and her husband retired to their room early to avoid exposure to smoke, as the hotel offers exclusively non-smoking accommodations.

“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.