Footnotes

• Contributors AgJ was involved in conceptualisation, development and testing of the device, and wrote the paper. RL was involved in conceptualisation, development and testing of the device, and contributed to writing the manuscript. RS was involved in conceptualisation, development and testing of the device, and contributed to writing the manuscript. PS was involved in testing of the device and contributed to writing of the manuscript. ArJ and TG developed the app and contributed to writing the manuscript.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Provenance and peer review Not commissioned; externally peer reviewed.