When the D928 is installed, the control panel alternates between Phone Line 1 and Phone Line 2 to send its first report. For example, on Day 1, the control panel attempts to communicate on Phone Line 1. On Day 2, the control panel switches and attempts to communicate on Phone Line 2. When the control panel is reset or powered on or off, the next reported event always attempts to call out on Phone Line 1 first. If Phone Line 2 (secondary) is not in service on Day 2, the control panel switches to the primary phone line to send the report.The Bosch Security System control panels use the D928 Dual Phone Line Switcher to transmit over a second phone line when the primary phone line has a fault. The control panel monitors the primary line and the D928 monitors the secondary line. If a signal is generated and the control panel senses that the primary phone line is bad, it will attempt to use the secondary phone line to send the message.
Part numbers D7212B, D9112B, D7212B1, D9112B1, D7212, D7412, D9112, D9124, D9412, D7412G, D9124G, D9412G, D7412GV2, D9124GV2, D9412GV2, D7412GV3, D9412GV3, D7412GV4, D9412GV4, D928,