This is probably not the security droid we're looking for.

The egg-shaped robot, known as the K5 Autonomous Data Machine, drew sympathy and jeers on Monday after it stumbled down a set of steps and into a fountain at Washington Harbour, an office and retail complex in the Georgetown neighbourhood in Washington, D.C. The photos were widely shared.

The robot is 1.5 metres tall, weighs 136 kilograms and can travel up to 5 kilometres per hour. It bears a passing resemblance to R2-D2 or perhaps a Dalek.

The K5's pop-culture cousin is clearly RoboCop. It is equipped with, among other things, thermal imaging, automatic license plate recognition and a video camera. Knightscope, the California-based maker of the robot, said its machines can be "an additional set of intelligent eyes and ears" for security and law enforcement. Its clients include data centres, hospitals and shopping malls.

Knightscope responded to the robot's social media fame with its own Twitter jokes on Tuesday, tweeting: "Security robot, yes. Submarine robot, no. Got it. K5."

William Santana Li, the company's chief executive, said in an email that what happened was under investigation and that a new robot would be delivered free this week to Washington Harbour.

While some Twitter users theorised that the K5 committed roboticide, a simpler explanation was provided by Michael Bailey-Van Kuren, the C. Michael Armstrong professor of engineering and interactive media at Miami University in Oxford, Ohio.

"Like with any technology, you can have a fault condition and an error can occur," he said.

Technology is advanced well enough to direct autonomous devices away from obstacles, he said, noting that even Roomba, the vacuuming robot, has sensors to avoid stairs. That the K5 did not detect the stairs was an anomaly, he said.

Knightscope said on its website that its models "guide themselves through even the most complex environments."

If the K5 were able to feel embarrassed, it could take comfort in science fiction long foretelling that stairs will be a great nemesis of security robots.

In the movie RoboCop which opened in theatres 30 years ago on Monday, an enforcement droid known as the ED-209 falls down a flight of stairs and struggles like a turtle on its back.

This is not the K5's first brush with media notoriety. It made headlines in April in Mountain View, California, when a man who was drunk knocked down a model, scratching it. Last year, another one ran over a 16-month-old boy at a Palo Alto, California, shopping centre, causing minor injuries, according to television news accounts.

It appears Paul Blart of the Mall Cop movies still has job security.

The New York Times