An alarm means an engineered system: aerobic treatment, a pump chamber, or a mound. It usually indicates a high liquid level from a failed pump or a power interruption. Reduce water use and call the same day.
More detail
Conventional gravity systems have no moving parts and no alarm. If yours has one, the site could not support a conventional field and an engineered system was permitted instead. That changes both the diagnosis and the maintenance obligation. The alarm is nearly always a high-water float in a pump chamber. The common causes are a failed effluent pump, a tripped breaker or GFCI, a stuck float switch, or a power outage long enough for the chamber to fill. Silencing the alarm does not fix it, and continued water use with a dead pump fills the chamber until it backs up. The immediate step is to reduce water use to a minimum and check the breaker. If the breaker is fine, the pump or the float needs service. The system types behind an alarm. An aerobic treatment unit injects air to support aerobic bacteria, which treat effluent far more thoroughly than a conventional tank and require a working blower plus periodic service. A mound system pumps effluent up into an engineered sand bed above grade, used where the water table is high or soil depth is shallow. A drip distribution system doses effluent through small-diameter tubing on a timer. All of them carry an ongoing service requirement that conventional systems do not, and many counties require a maintenance contract as a condition of the operating permit. Electrical cost runs $10 to $30 a month for a blower or pump. If you inherited one of these with the house, get the operating permit and the service history from the county health district and find out when the last service visit happened. Engineered systems fail quietly when nobody is servicing them. Engineered systems are concentrated in the parts of Franklin, Delaware, Licking, and Fairfield counties where soil depth or the water table ruled out a conventional field. Central Ohio sits on flat-lying glacial till with dense clay subsoils that drain slowly and perch water above the till rather than letting it through. If your lot has one, that is why, and it is not a decision a later owner can reverse.