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San Francisco sidewalks are Sisters Sex Scandalabout to see more robot traffic.

Yelp's Eat24 food delivery service is teaming with startup Marble to start dispatching automated couriers in the city on a trial basis.

At around three feet tall -- depending on the size of the attached cargo bay -- Marble's boxy bots are much bulkier than the Starship Technology ones already zipping around various cities. Whereas Starship's look more like sleek futuristic pods, Marble's more closely resemble an office printer.

That also makes them an imposing presence on narrow sidewalks.

For now, the robots will only travel with a human handler in tow, and they're sticking to relatively flat neighborhoods to avoid the city's famously daunting hills.

Marble has been compiling a three-dimensional map of San Francisco sidewalks for months in anticipation of the launch. The bots are also equipped with an array of sensors to ensure they don't, say, mow down inattentive texters.

The bot's storage container can only be unlocked with a code that is texted to the order recipient upon its arrival. The delivery mode is currently opt-in only -- robots will not be forced on anyone.

Sleek automated pods like these are becoming a more common sight in the Bay Area and Washington D.C. as food delivery startups toy with the idea of replacing their armies of gig-economy semi-employees.

Unlike independent contractors, robots don't demand things like reasons they were "deactivated" -- the Orwellian euphemism on-demand startups use for firing people -- or reasonable pay. That could help the growing cadre of on-demand startups ease costs in a notoriously brutal business model.

So far, only Virginia has passed a law to formally legalize delivery by bot, however. While San Francisco politicians have discussed potential legal frameworks, the bots currently operate under a city permit that costs $66 for every side of a block in their routes.

Marble also announced Wednesday that it raised $4 million in venture capital.

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