Facebook is offering to pay its users for personal information including recordings of their own voice, in a rare example of internet companies directly compensating people for collecting their data.

The recordings, made through its new market research app Viewpoints, will help to train the speech recognition system that powers Facebook’s Portal devices, which rival Amazon’s Echo speakers and its Alexa virtual assistant.

Makers of smart speakers including Facebook, Amazon, Apple and Google faced criticism last year when it emerged that they were routinely sending users’ voice recordings to human moderators, without revealing the practice to customers or obtaining their consent.