A start-up that lets residents monitor who drives in and out of their neighbourhood was among the companies revealed at a Silicon Valley event on Monday.
Flock's sensor, which it offers for $50 a year per house, logs the number plates of every car that drives into a street and takes a picture. The sensor could eventually provide facial recognition.
Residents of monitored neighbourhoods can opt-out of being tracked - but visitors, or people passing through, cannot.
Flock is backed by Y Combinator, a start-up “incubator” which in the past has funded successes including Dropbox, Reddit and AirBnB.
A privacy expert said he believed the data collection to be legal according to US law, but that the idea could ignite a debate about the "right to be left alone in public”.
“One of the great weaknesses in US privacy law is that we only protect against intrusions into private areas, not public spaces,” said Albert Gidari, director of privacy at Stanford Law School's Center for Internet and Society.
"Public roads through neighbourhoods, licence plates, pedestrians on public sidewalks etc all are fair game," he said.
The data is only made available to “neighbourhood leaders”, Flock says, and is a tool that could be used to fight crime.
To date, one person has been convicted thanks to evidence captured by the device.
“An unfortunate individual drove into one of our [monitored] neighbourhoods,” explained Garret Langley, chief executive and co-founder of Flock.
"He put a nice road bike in the back of his car, and drove off with both the window down and the trunk open.
"Not only do we have footage of his licence plate, we have a picture of his face and a picture of the bike in the back.”
‘Not our data'
The technology was shown off at Y Combinator’s Demo Day, the twice-yearly event at which entrepreneurs pitch their companies to several hundred investors.
Flock’s devices are being trialled in seven neighbourhoods in and around Atlanta, with more locations across the US currently being considered.
Also at Y Combinator's Demo Day on Monday
- Relationship Hero is a service that steps in to offer advice on your relationships - personal or professional. The company lets you discuss issues over the phone or via a chat bot, and will even make suggestions over how to write your messages. “This isn’t therapy,” the team said.
- Feather is a company offering quick-turnaround furniture rental “for millennials and businesses”. The firm will deliver - in San Francisco and New York - big ticket items that the company believes people no longer want to buy.
- Targeting disgruntled Uber and Lyft drivers, Mystro makes is easier to switch between various ride-sharing apps to get more rides and better, more valuable fares. It was created by Herb Coakley, a former Uber driver. “I probably drove some of you around,” he told investors.
- 70 Million Jobs was created by Richard Bronson, a man jailed for securities fraud tied to his work at Stratton Oakmont, the firm immortalised in the film The Wolf of Wall Street. Now his start-up seeks to make it easier for people with a criminal record to find work by using algorithms to match skills with firms looking to recruit quickly.
- Darmiyan is a company that says it uses machine learning to detect signs of Alzheimers more than 15 years before symptoms emerge. It expects to have approval from the US Federal Drug Administration within the next year.
A second day of presentations takes place on Tuesday
Residents in neighbourhoods being trialled by Flock can opt-out of being tracked, but visitors to those locations - or simply people passing through - have no way of stopping the technology from logging their movements.
“Should there be? I would leave that up to the neighbourhood to decide,” Mr Langley told the BBC.
“We believe that our job is to provide the neighbourhoods with the technology to protect themselves as they see fit.
"We don’t want into get into the business of making decisions about privacy and how this technology is used beyond the original use case.
“It's not our data - it’s the neighbourhood’s data - and we delete it after 30 days.”
Stanford’s Mr Gidari said the technology perhaps highlighted one instance where long-existing laws may not have taken into consideration the types of technology on offer today.
"As these systems become more available and new platforms for capturing imagery become cheaper to deploy, we may yet revisit the issue of whether there is a right to be left alone in public, to be obscure or anonymous, or to be free from collection and storage in other's systems."
He added: “A few states have laws that prohibit the collection of biometric information - facial recognition would raise the issue.”