Like so many classic Western anti-heroes before him, he rolled (literally) into town with a singular goal in mind: cleaning up the streets, which had become a gritty hotbed of harassment, vandalism, break-ins and grift.

The only difference was that he was a slow-moving, 180kg robot with a penchant for snapping hundreds of photos a minute without people's permission, and this was San Francisco's Mission District in 2017.

What could go wrong? Quite a bit, as it turns out.

In the past month, his first on the job, "K-9" — a 1.5m-tall, 1m-wide K5 Autonomous Data Machine that can be rented for US$6 an hour from Silicon Valley startup Knightscope — was battered with barbecue sauce, allegedly smeared with feces, covered by a tarp and nearly toppled by an attacker.


As if those incidents weren't bad enough, K-9 was also accused of discriminating against homeless people. It was those troubling allegations, which went viral, that sparked public outrage and prompted K-9's employers — the San Francisco chapter of the SPCA — to pull the plug on their robot.

"Effective immediately, the San Francisco SPCA has suspended its security robot pilot programme," Jennifer Scarlett, the organisation's president, said. "[It was] an effort to improve the security around our campus and to create a safe atmosphere for staff, volunteers, clients and animals. Clearly, it backfired."

SPCA officials said the robot was hired to patrol the parking lot and footpath outside the animal shelter after the building had been broken into twice and employees had become fed up with harassment and catcalls. The robot, they said, would be able to snap photos, record security footage, and then notify shelter employees or police during an emergency.

The backlash began after an animal shelter spokeswoman seemed to suggest that the robot was an effective tool for eliminating homeless encampments outside the SPCA. SPCA officials now say they didn't mean to imply that they wanted to be rid of the homeless. Nevertheless, a public outcry, complete with calls for the robot's destruction, quickly ensued. "Robot wages war on the homeless," a Newsweek headline read. In recent days, SPCA officials said, they've received hundreds of messages encouraging people to seek retribution against the animal shelter. So far, officials said, the facility has experienced two acts of vandalism.

K-9 is not the first Knightscope machine to have a short-lived security career. In July, a robot patrolling Washington Harbour ended up in a fountain, its cone-shaped body halfway submerged.