This read-write TruthValue turns the generation of the c3gModemDownNotif notification on or off, which fires when the modem goes down. An admin enables this to be alerted the instant a cellular modem becomes undetectable, which is often the first sign of a hardware fault or a dislodged modem card. For example, enabling this notification on a primary cellular backup link ensures the admin isn't caught unaware the failover path has silently died.