Filters, also known as traps, are security devices used by cable companies to ensure that customers receive only the services they pay for. Customers cannot remove filters themselves as they are securely installed. Authorized service technicians can remove traps as necessary when a customer upgrades their service.
Filters are frequently used to block premium movie channels, such as HBO, from being viewable on a non-subscriber's television. When the channel is purchased, the filter is removed, allowing televisions to display the audio and video for the particular network. Filters are also used to block all video services for customers who only purchase Internet access.