Search on the web for “best time to book airfare” for the lowest price and you’ll find many conflicting answers, but there is no magic formula.

The best approach: sign up for “airfare alerts” by email. Do a search for the phrase on the web and you’ll find many options from reputable companies that send email alerts.

These alerts all work a bit differently. Some only allow you to track specific dates, while others allow you to specify “to” and “from” specific airports because a fare from Baltimore Washington International (BWI) might not be as ideal as one from closer-in Washington National DCA. Most alert systems treat “nearby” airports as equal, but tell that to someone who doesn’t want to trek out to Baltimore or Dulles when National is just a Metro ride away.

Take note that the lowest fares are often on airlines that people hate to fly (because they charge for carry-on bags and seat assignments), so look for a service that allows you to eliminate alerts from airlines you’d never fly even if they were free (Airfarewatchdog.com does allow specific airline choice).

Sign up for several alerts: All online travel agencies do not show the same prices. I recently saw a fare from New York to South Africa offered on Delta and KLM for $200 less round trip if booked on Priceline, versus the same flights, dates and airlines if booked on Orbitz, Expedia, Travelocity or on KLM’s or Delta’s own websites. It’s worth searching more than one site.

Twitter is another great source for short-lived airfare deals. Follow the #airfare hashtag where over a half-dozen accounts tweet out unadvertised deals. The #flights hashtag is also useful. Follow the accounts you find there.

Once you’re signed up or following, you have to act. An airfare from L.A. to Singapore (this is a recent example) might go down, unadvertised, to $398 round trip including tax on Singapore Airlines, whereas other airlines were charging $800 for the same travel dates but on less desirable connecting flights. But that fare, even if it’s good over several months, might appear for just three or four hours, and then it goes back up to $800.

Since airlines now allow you to pay for a fare and cancel within 24 hours without paying a fee, the strategy is to book to hold it and then get your friends and family on board and sort out hotels.

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George Hobica, Airfarewatchdog.com

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Storytrail.co

Here’s a spunky video city guide that will take you sightseeing in New York, San Francisco, Lisbon, London, Los Angeles and Rome.

>> What it does: Jason, your friendly host and urban explorer, recounts each city’s history by walking the viewer to points and places of interest.

>> What’s hot: The videos are short, informative and easily digested by an armchair traveler or someone who wants to visit curious corners, bars, architecture, colorful historic hotels, bookstores, street art and more. I like the site’s organization: Watch the video trailer for each city and learn what’s to come. A trail map at the bottom of each video outlines which stories are next on your visual meander through the city. This site is for you if you love history or are interested in the stories behind popular street murals in Venice Beach, painted caves in Rome or an 18th-century New York tavern. It’s worth noting that there was no buffering or site crashing while I was watching the videos.

>> What’s not: It was difficult to scroll horizontally through the videos for a given place, such as San Francisco’s Chinatown. The trail map tells you which video is next, but clicking on it didn’t get me a video. How about making the trail link to videos?

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Jen Leo, Los Angeles Times