Customers are being tracked by bugging devices fixed to their shopping trolleys and baskets as they shop in an Auckland supermarket.
New World Victoria Park is trialling PathFinder tracking devices to obtain information on shoppers' habits as they select their groceries.
But the customers are not told their movements are being traced.
The 13cm-long black rectangular plastic boxes contain batteries and GPS satellite tracking technology, and are bolted under the lip of some baskets and to the front of some trolleys at the Freemans Bay store.
The trial is believed to be a first in New Zealand.
But the system is in use overseas, where it has been criticised as introducing a "big brother approach" to consumer research that influences store layout, the positioning of products on shelves and the placement of advertising and promotions in stores.
New World Victoria Park owner and operator Jason Witehira said the technology gave him an overview of what was happening, and where, in his store.
"If I wanted, I could log on and watch our baskets and trolleys moving around our store," he said.
The trial, which started last month, had already resulted in changes to the store's layout.
Developed by Australian company NextGen, the PathFinder technology provided an "unprecedented" level of accuracy, said spokesman Neil Rechlin.
"Through being able to track the trolley movements, a retailer is able to tune the store environment to better meet the shoppers' needs.
"For the store manager, the technology allows him or her to ensure sufficient trolleys and baskets are available, shelves are correctly filled at the right time of day and the right number of checkouts are open."
When the Weekend Herald visited the store, there were no signs telling customers of the technology.
Shoppers spoken to said they were not concerned at being monitored, but would prefer to know.
University of Auckland senior marketing lecturer Mike Lee said the trackers could upset some people.
"I think customers need to be informed that they will be tracked or monitored when they enter any environment," he said.
"From there, customers may choose to enter or not and I believe the majority of people would not care too much these days, since all of our purchases are tracked in some way or another, [for example] whenever we use a credit card or rewards system like Fly Buys and Onecard.
"A few may see this as another instance of Big Brother encroaching on their lives, but retail environments are private enterprises and therefore the private business owner can establish whatever security devices they deem necessary on their premises."
A Privacy Commission official said it was important the GPS data did not identify individuals.
"If this is the case, our view is that the supermarket is allowed to do this, but we feel it should tell its customers. It is not a legal obligation but you could say it is a moral one.
"Customers should be told that their movements using a trolley or basket are being tracked around the supermarket.
"If the supermarket did inform its customers ... they would then be more inclined to feel reassured and continue to shop with it."
Consumer New Zealand chief Sue Chetwin agreed.
"It looks a bit spooky but as long as they are not filming you so as to breach your privacy ..." she said.
"It could be quite useful information that the supermarket is collecting in terms of what customers want so it might provide better products or different sorts of products."
Mr Rechlin said the technology tracked the baskets and trolleys, not the people pushing them.
"We have no idea who is pushing the trolley. It doesn't track Mrs Jones, for example, as she shops in the store.
"What it does is collect information on where the trolley has been, at what time of day, how long a customer spent in a particular section of the store, without tying any information to an individual."
A representative of New World's parent company, Foodstuffs North Island, which also operates Pak'n Save and Four Square, said the company would consider using the technology in other stores.
A spokeswoman for the rival Countdown supermarket chain said the company did not use such technology in its stores.
• Kelly Thompson, Ponsonby: "It doesn't really bother me. I think some people could be offended that there is no notice of it. I had no idea, but I think from a consumer's point of view, people like to know."
• Brett Cammell, North Shore: "If it makes for more efficient shopping and easier ways of finding things, I think it's great."
• Durrell Williams, Ponsonby: "I think if they are able to provide a better service somehow through that, then it's not a bad thing. It's probably a good idea to have signs, but I have no problem with them knowing what I am buying if it means they stock more of what I want."
• Emma, Ponsonby: "I think they probably should tell customers. I think some people probably would (want to know) when they are being tracked. There should be some sort of sign."