Museums are tracking visitors’ movements using their phone’s wifi to see what the most popular exhibits are.
They claim the information will help them to improve exhibition layouts and reduce congestion.
But privacy campaigners have condemned the move as the information is often gathered without a person’s consent or knowledge.
A freedom of information request by tech site Gizmodo revealed that the Natural History Museum and the National Railway Museum (part of the Science Museum group) routinely tracked visitors' movements using their phone wifi signal.
The National Gallery also used the technology in recent pilot scheme.
The signal can be picked up from phones with wifi switched on – even if it is not connected to the network – and visitors appear on computers as coloured dots.
Through the technology the National Gallery scheme found that the room with 16th century Venetian paintings, including Titians and Tintorettos, was the most visited space after the entrance halls.
The National History Museum would not reveal their findings but said the data was used to recommend quieter routes on busy days.
There was an outcry in 2017 when it was revealed that Transport for London tracked Tube passengers using wifi to analyse operations at stations.
But analysts say this technology is often used without knowledge or consent in shops to learn about customer behaviour.
John Stevenson, an analyst at Peel Hunt, told The Times: "This data does not identify individuals, or give organisations access to any personal information.
"It's far more insightful data than old-fashioned surveys."