The 900A alarm filters are designed to allow residential alarm panels to take control of the main phone line via the RJ31X or RJ38X connector. The 900A blocks DSL service to the alarm panel while providing uninterrupted DSL service to the household telephone wiring. This inline filter is designed to plug into a RJ31X jack, including other similar jacks up to RJ38X. Customer installable Automated alarm dialer compatible high-speed Internet device FCC Registered; Complies with Part 68, FCC Rules UL Listed; Standards - 1863 Dimensions: 3.0inch L x 1.0inch H x 0.8inch D