When it was time for Omni Hotels and Resorts to start a new round of renovations, executives made a point of installing more electrical outlets and better bathrooms.

The impetus for those upgrades? Complaints from travelers on review websites such as TripAdvisor.

“They certainly are not shy,” Jon Hunter, vice president for operations for Omni Hotels and Resorts, said of the reviewers.

“It was obvious we didn’t have enough fixtures in the bedrooms that had electrical outlets,” he added. “As we scoped out new constructions or renovation projects, we certainly kept that in mind.”

As hotels in the United States continue on a surge in spending on renovations, an ever-more-important factor driving this investment is the growing clout of review sites such as TripAdvisor and Yelp, and booking sites such as Hotels.com.

Hotel brands are reading what travelers say about them — and their competitors — and planning their investments accordingly.

“It’s become a widely understood source of input for capital expenditures,” which are projected to hit a record $6 billion this year, said Bjorn Hanson, a professor at New York University’s Preston Robert Tisch Center for Hospitality, Tourism and Sports Management.

That is partly because people are quicker to complain on review sites and on social media, Hanson said. “Rates have gone up, so guests are expecting to see that reflected in the quality.”

Often, disgruntled guests will not say anything to managers, making the monitoring of websites all the more important, said Hermann Elger, general manager of the St. Regis New York.

“People use that much more as an avenue to give feedback and let us know when something didn’t go right,” he said.

Technology providers work with hotels to sift through thousands of reviews, often using algorithmic software, to find areas of trouble — and weed out those complaints that are not genuine. Common complaints often have to do with water pressure in the showers, slow Wi-Fi, uncomfortable beds, dated televisions and the location.

Lights are a particular issue with guests. For the St. Regis, it was the switches.

“It’s very common for guests to be frustrated about the number of lights and switches they have to turn off,” Elger said. After reading complaints, the St. Regis included a centrally located master light switch in guest rooms.

At the Loews Regency in New York, Paul Whetsell, president and chief executive of Loews Hotels, said that, as in the Omni case, the design team paid a lot of attention to guest complaints about bathroom lighting, among other elements.

“Sometimes designers design our bathrooms to look good but not necessarily be totally functional,” he said. “Lighting is something that’s mentioned on social quite often.”

The travelers say a poor review on TripAdvisor sometimes can be the only way to get a manager’s attention.

Janae Lee, an executive at a technology company and a frequent traveler, writes reviews often. “I do it for two reasons — to give feedback, and so others like me don’t find themselves in the same situation,” she said.

On a business trip to New York, Lee booked a room at a hotel where she had previously stayed, only to find that the restaurant, Starbucks and sundries shop all were gone. On a more recent trip to San Francisco, she ran into a similar lack of dining options when arriving late at night.

“My first line of defense normally is to reach out to the property directly,” she said. “They didn’t resolve the concern.”

Her attempts to contact the corporate headquarters and even one of the company’s marketing executives did not yield responses, so Lee went online to express her displeasure.

Details about the location and the neighborhood can take on a different tone when described by guests as opposed to a hotel’s marketing department, said Greg Hartmann, managing director at Jones Lang LaSalle in the hotel asset management and advisory group.

“The website might say, ‘We’re only four blocks from the convention center,’ as a positive,” he pointed out, but online reviewers would be quick to say if those four blocks are clogged with traffic, hard to navigate or feel dangerous.

This feedback from travelers is making hotels respond.

“As an industry, I think when TripAdvisor first started we looked at that as a channel that didn’t have a lot of credibility,” Hunter said. “That has certainly changed.”