Waymo locks down and alerts police after passengers bring ghost gun inside

Two teenagers have been arrested in San Francisco after their driverless Waymo taxi detected they had a firearm, pulled itself over to the side of the road, and called the police.

Officers who arrived at the scene discovered a loaded, AR-style "ghost gun" — an untraceable weapon assembled from parts without serial numbers — along with suspected marijuana and mace spray inside the vehicle.

The incident happened shortly before 4 a.m. on 3 September in the city's Richmond District, the San Francisco Police Department said. Officers conducted what they described as a "high-risk vehicle stop" to detain the passengers, a boy and a girl. Neither has been publicly identified because of their age.

While police did not name the autonomous vehicle operator in their public statement, a Waymo spokesperson confirmed that one of its cars was involved. The company said it remotely ordered the car to pull over after detecting "a violation of our terms of service involving a firearm," and immediately alerted emergency services.

How the vehicle or its remote operators detected the weapon remains unanswered. Waymo cars are fitted with internal cameras and audio sensors, but the company has not explained whether the rifle was spotted by an automated system or flagged by a human supervisor monitoring the cabin's video feed.

The two teenagers were taken into custody and booked into a local juvenile hall. San Francisco police said the investigation remains open and active.

This is not the first time a self-driving taxi has ratted on its passengers. In July, Waymo contacted police in San Mateo after two 15-year-olds were spotted drinking alcohol and shooting toy guns out of a vehicle's windows. Officers arrived to find the teenagers shooting Orbeez water beads, leading local police to post a light-hearted warning on social media: "Parents do you know where your teens are? Waymo does!"

Waymo, which began in 2009 as Google's self-driving car project before spinning out as an independent company in 2016, has rapidly expanded its footprint. The distinctive vehicles, topped with spinning lidar sensors, are now a common sight in San Francisco and Los Angeles. The company recently won permission from California regulators to expand further into areas like Orange County and Sacramento, and has launched paid services in San Diego, Denver, and Tampa.

But the absence of a human driver has also made the vehicles a target for bizarre behaviour and occasional vandalism. Last year, a man in downtown Los Angeles was arrested after climbing into a Waymo and trying to drive it away manually. In July, a shirtless man in East Hollywood was filmed climbing onto the roof of a stationary Waymo and dismantling its sensor equipment.