The CH1804/A and CH1809/A are line status detectors that are used to monitor line off-hook status for shared lines, or to detect a severed or cut telephone line. The CH1804/A is a single line monitor. The CH1809/A is a dual line device allowing two telephone lines to be monitored simultaneously and contains two CH1804/A circuits (See Figure1). For ease of convertibility, both devices share the same pin out configuration.