The 'free' wi-fi at Woolworths Group stores is set to make users spend more, after the South African retailer said its shoppers' movements would be monetised by Sydney data analytics startup Skyfii.

Over the next three years the ASX-listed firm's software-as-a-service platform will be fed information from the free wi-fi inside over 500 stores in the Woolworths portfolio.

Anybody who enters these stores with wi-fi enabled on their smartphones will now have their movements tracked by Skyfii, even if the device stays in their pocket. However, after they sign up for and access the store's existing free wi-fi service, Skyfii tracks not only their movements but their internet and social media use in real time.

Wayne Arthur, founder and CEO of Skyfii. Tim Wheeler

Skyfii, which made a $2.2 million loss on $1.7 million revenue in the first half of 2016-17, also analyses wi-fi use in the common areas of Westfield and Mirvac malls, from where it can send browsers marketing text messages or email offers to entice them into nearby client stores.

Its technology can also keep them in a store, with founder and chief executive Wayne Arthur giving the example of a customer shopping for suits in a department store Googling 'suits' and beginning to browse a competitor's e-commerce site.