In recent years, the unpredictability of terrorizing events has kept Americans on alert, wary of threats to their safety and well-being.

A gunman killed 58 people attending an outdoor concert in Las Vegas last year. School violence has become commonplace enough that some teens carry bulletproof backpacks. And last week, at least a dozen homemade pipe bombs were mailed to outspoken critics of President Trump and forced the evacuation of a shopping mall in New York.

Specific threats and a general sense of anxiety, security experts say, are causing more people to seek the services of private security firms; some are hiring bodyguards and drivers trained to protect them in case of peril.

At Pinkerton, a private security and detective agency founded in 1850, requests for executive security have increased 20 to 30 percent annually over the last five years, said its vice chairman, Tim Williams. And people are looking for safeguards in all areas of their lives that pose risks, experts say, including information technology and social media.