A data logger sits inside a refrigerator, freezer, cold room or shipping box and records temperature every few minutes, around the clock. Basic models store readings to download later; others display minimum and maximum readings, and connected models send data over Wi-Fi or a mobile network to a dashboard that alerts staff by SMS, app or email when a reading goes out of range.
Loggers fill the gaps that manual checks miss: nights, weekends, holidays and power cuts. They are standard in pharma and lab storage and increasingly used by restaurant chains and food retailers. For the data to be trusted, loggers should be calibrated, placed where they represent the stored product rather than the coldest or warmest corner, and reviewed regularly. Some use a probe in a buffer such as glycol to mimic product temperature rather than air temperature.
A diagnostic lab in Hyderabad might fit a connected logger to each reagent refrigerator. When a compressor fails at 2 a.m., the lab manager gets an alert and moves reagents to a backup unit before they warm up.