In order to estimate viewing patterns across all TV households, a carefully selected panel of private homes is recruited
> Once a household has been recruited to the BARB panel, Kantar Media fits every TV set in the home with a meter. Software meters are also installed on laptop and desktop computers, and tablets. In order for the meter to know who is watching, each member of the household over the age of four is assigned a button on a special remote control. If they enter a room while the television is on they must press their designated button to register their presence and press it again when they leave to show they are no longer watching.