The new robot delivery service is a result of a partnership between Yelp and the small startup Marble, founded in 2015 by three former Carnegie Mellon University students.

Starting Wednesday, residents of San Francisco’s Mission and Potrero Hill neighborhoods who order meals from Yelp’s Eat24 food delivery service will have the option of having a robot shuttle them dinner to their doorsteps. Yelp (YELP) bought Eat24 in 2014 for $134 million to expand beyond online business listings.

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People living in the eligible San Francisco neighborhoods who order food through Yelp Eat24 will receive a text message explaining the new test delivery program and asking them if they want to participate. After users say yes, a robot will be dispatched to the appropriate restaurant where staff will prepare the food and then stow it in a compartment in the robot for delivery.

The robot resembles an oversized fax machine on wheels.

Marble’s robots roll on sidewalks about as quickly as humans on foot. Sensors and cameras help them avoid curious pedestrians or barking dogs. If it approaches a stationary object like a mailbox, it steers clear and rolls by. When it approaches an intersection, it pauses to check for incoming cars and then crosses.

“I don’t want to live in a world with robots that are getting in my way,” Marble CEO Matthew Delaney said.

Customers are sent a password to open the robot’s compartment to get their food. Instead waiting for the doorbell to ring, customers are notified that the robot has arrived—it can’t climb stairs—by text message.

Marble’s small fleet of robots have been continuously mapping the city streets in the neighborhoods where they operate and have learned which sidewalks are the most heavily trafficked during certain times, Delaney said. Based on that, they can alternate their routes to get to their destinations more quickly, he explained.

Currently, only five restaurants are participating in Yelp’s Eat24 robot delivery program, but Delaney expects that more will sign up in the future.

To be sure, the robot delivery service is merely an experiment to see whether people are interested in automated food delivery. During the test, a Marble employee will accompany the robot to ensure that all goes smoothly.

It probably helps to have someone nearby to ensure that no one vandalizes the robot or steals it. Marble did not disclose how much the robots cost, but they’re likely very expensive considering the technology and development time that goes into them.

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The economic viability of delivery robots is unclear. But Delaney said that the owner of Truly Mediterranean, a participating restaurant, is excited to use the robots because of the potential to sell more falafels.

Delaney said Marble’s goal is to create a fleet of robots and partner with other companies like Yelp to put them into use. These partner companies would pay Marble a recurring fee. Marble does not disclose its revenue, if any.

Marble has raised $4 million of funding from investors including Eclipse, Maven Ventures, Amplify Partners and Lemnos Labs.

Delaney thinks that solving the problem of using robots to delivery anything and everything to homes and businesses would be a major accomplishment. The so-called “last mile,” creating an economical and efficient system to automate doorstep deliveries, would save money, time, and free people to do other more important things.

“This is the biggest opportunity for robotics in front of humanity right now,” Delaney said.