Body worn cameras that can be used for both overt and covert surveillance. Some are 1 piece systems whilst others are 2 piece systems (usually a camera with a button lens & handheld digital video recorder).
The 2 part body worn camera systems are usually for covert surveillance operations and are a favourite of mystery shoppers, private investigators and journalists etc. They will consist of a small handheld digital video recording unit, which will normally be stored in an inside jacket pocket or a bag for example, you would have a short cable running to a button camera which could be hidden about your clothing somewhere.
The 1 piece body worn camera units are for overt surveillance operations and are commonly worn by police officers and security staff etc. These overt body cameras are designed to immediately alert the subject that they are being recorded and so provide safety for the subject and the body camera user/wearer.