Either way, that congenial vibe is one of two big things differentiating Cobalt from other commercial robots—especially ones from Knightscope, another Silicon Valley startup and the current leader in developing security bots. Knightscope's flagship, the K5, started patrolling malls, offices, and schools in 2015, and looks pretty intimidating when it's not nose-diving into fountains. Aggressive, even—like a cross between a Dalek and Bullet Bill. The upshot is that Knightscope's robot resembles hired muscle, while Cobalt Robotics' looks like the kind of machine you might ask for directions.

The second thing Cobalt has going for it is telepresence. Most of the time, Cobalt patrols autonomously, detecting people, dodging obstacles, and flagging anomalies on the fly. But if it spots something unusual, it alerts a remote operator. The robot can then ask its human partner questions like "Is this a person?" to improve its computer-vision algorithms, or allow that carbon-based lifeform to assume control of its movements and display their face on its forward-mounted touchscreen.

This is exactly what happens around 8:30 pm, halfway through the patrol route. Cobalt spots a woman sitting quietly at the far end of the office, staring at a computer screen. The robot alerts Shiloh Nordby, Cobalt Robotics' lead pilot, who is overseeing an undisclosed number of robots from the company's headquarters in Palo Alto, some 35 miles away.

Lee and I watch from perhaps 40 feet away as Nordby takes control of the robot. He approaches the woman slowly, parking Cobalt a few feet to her right, just beyond her field of view.

"Hi there," Nordby says. No response. Maybe she didn't hear him.

"Hi there," he says again, louder this time.

"Oh, hi! How are you," the woman replies, turning quickly in her chair.

"Good, thanks. My name is Shiloh. I'm with Cobalt Robotics. Do you mind badging in on the screen?"

"Sure!"

Nordby scoots the robot to within arm's reach of the woman, who grabs her employee ID, raises it toward the screen, and pauses. She seems confused about where to put her badge.

"Oh, just place it right below the screen," Nordby says.

"OK, right here? Oh. Oh! Wow, OK," she says, as the screen gives the all-clear.

"Thanks," Nordby replies. "Have a good night."

"Thanks, you as well."

"Thank you!" Lee shouts at the woman, alerting her to our presence.

"Oh, no problem," she says. "That was awesome!"

Lee swears Cobalt's badge-in interaction wasn't staged. In fact, in the four months Cobalt has been monitoring Yelp's offices, he's never seen it do this in person. Lee occasionally pops in unannounced to join the robot on patrol, but he mostly keeps tabs on its performance through a weekly "instance report," prepared by Cobalt Robotics. The dossier includes details like the number of people detected and authenticated, the robot's schedule and patrol routes, and detailed descriptions of significant incidents from the preceding week.

Like a recent report of a rogue pair of microwave thieves. In timestamps, video stills, and transcribed conversations, Cobalt told Lee how it spied a couple of Yelp staffers schlepping an appliance from the office. Lee showed me a still of the video Cobalt captured of the incident. The pair did look suspicious, but they had merely burned something in the microwave and were moving it outside to air it out.

Lee says he's quite satisfied with the 'bot. "I wanted a super-capable machine, full of sensors, coupled with telepresence to help with customer service, creative problem solving, and negotiating all sorts of things people usually deal with every day," he says. "So far, it's functioning exactly the way I envisioned. It operates on its own, and the employees, once they've interacted with it a few times, barely notice it."

Robotic Symbiosis

Friendly—and subtle—human interaction is a bigger deal than you might think. Especially for robots, and especially right now. "I think that 20 years from now, robots moving among us will be very common—people aren't even going to notice whether they're there or not," says roboticist Manuela Veloso, who oversees Carnegie Mellon University's machine learning department. But first, she says, machines must earn humanity's trust.