BulletHD PRO2 Instruction Manual page 4

4.Camcorder on Vented Helmet
5.Camcorder on Handlebar
6.Camcorder on Non-vented Helmet
Using BulletHD for Water Sports
Remind you to put some silicon grease to the rubber O-ring from time
to time, especially before using underwater. Make sure the rear cap ③
was closed tight.