Most digital controllers allow high and low alarm limits with a time delay. For a chiller holding 2 to 4 °C, a high alarm might be set a few degrees above the normal range, with a delay so a single busy service or defrost does not trigger it. The alarm usually beeps and flashes on the display, and on some systems also triggers a relay for a remote buzzer, SMS or monitoring platform.
Low alarms matter too. A vaccine refrigerator that drops below +2 °C can damage stock as surely as one that runs warm, and a chiller running near freezing can spoil produce. Door-open alarms and probe-failure alarms are common extras.
An alarm only helps if someone acts on it. Kitchens and pharmacies should decide who responds, what they check first (door, power, defrost, condenser) and how excursions are recorded. Where power cuts are frequent, an alarm or data logger with battery backup ensures that outages are captured even when the cabinet itself has no power.