Presumably their ethical approvement was about considerably more than just potential physical danger of putting on the device for 10 minutes? Of course ethics

Presumably their ethical approvement was about considerably more than just potential physical danger of putting on the device for 10 minutes? Of course ethics does need to make sure that the testing isn't going to harm the participants directly, which is nice and simple in your example, but it also needs to make sure that any measurements will be stored (and anonymised) in ways that conform to your friend's country's healthcare data laws. It needs to make sure there are adequate data protection plans. It needs to ask questions like have they considered ways in which they might accidentally create a device with racial bias (the way pulse oximetres are often worse at reading the blood oxygen level of people with dark skin as they were made by and tested on the fingers of white people). Etc.