Automatic transfer switch (ATS)
An automatic transfer switch monitors utility power and switches the house to generator power without human action — it signals a standby generator to start, transfers the load once output is stable, and transfers back when the utility returns.
The ATS is what makes a home standby system hands-off: the whole sequence, from outage to restored power, typically takes 10–30 seconds and works when nobody is home.
ATS models are rated by amperage (100 A or 200 A for whole-panel service entrance installations) and many include load-shedding modules that drop low-priority circuits, letting a smaller generator protect a larger panel.