Inside his gadget is a simple temperature sensor, an ATtiny841, a very nice home-made PCB, a buzzer, an LCD ... he’s going to add a low-temperature alarm too, which will add a second alarm ...

It runs on mains power and uses a 100dB piezo buzzer for ear-splitting ... If the Arduino loses sight of the DHT22 temperature sensor inside the freezer, then the alarm sounds continuously.

It triggers buzzer alarms when a temperature exceeds the alarm threshold. It also supports device exception alerts, image enhancement, laser Pointer and cold/Hot spot trace. Dahua DH-HAC-T1A51-U 5MP ...