* "The strap and/or adhesive mounts could damage the helmet, especially if they’re installed less than perfectly."
* "the larger problem is the camera itself. A helmet is designed to have a surface without protrusions, and a camera represents a significant one. / ... "Anytime you add an external component to a helmet, you can change the performance of that helmet," says [Ian] Hall, [Consumer Product Safety Commission engineer]. "A helmet-mounted camera may become a projectile if it detaches in a crash, but a camera that remains attached could focus the forces applied to the rider’s head, increasing the risk of injury."
And from a Specialized helmet owner's manual: "Do not attach anything to your helmet, including mirrors or lights."
I've seen it in a few places. I dug up some notes:
The following is from: "The Do's and Don'ts of Bike Helmet Care" at Consumer Reports (15 April 2017) https://www.consumerreports.org/bike-helmets/the-dos-and-don...
* "The strap and/or adhesive mounts could damage the helmet, especially if they’re installed less than perfectly."
* "the larger problem is the camera itself. A helmet is designed to have a surface without protrusions, and a camera represents a significant one. / ... "Anytime you add an external component to a helmet, you can change the performance of that helmet," says [Ian] Hall, [Consumer Product Safety Commission engineer]. "A helmet-mounted camera may become a projectile if it detaches in a crash, but a camera that remains attached could focus the forces applied to the rider’s head, increasing the risk of injury."
And from a Specialized helmet owner's manual: "Do not attach anything to your helmet, including mirrors or lights."