Hi, I'm Waldemar,
The text below is from Smeg fridge user manual:
"The alarm sounds to warn of the following:
1. The fridge door has been open for more than a minute (continuous buzzer with relative red light on)
• Press the alarm button or close the fridge door to deactivate the buzzer and switch off the red light.
2. The temperature inside the refrigerator or freezer compartment is too high (intermittent buzzer, flashing display and light on)
• Press the alarm button the buzzer.
• The red light and the flashing temperature on the display turn off automatically when the refrigerator compartment or the freezer compartment reach the previously set temperature. If the freezer compartment does not reach the required temperature within 24 hours of the alarm being turned off, it will sound again."
I recommend to check first the door switch. If the switch is locked or malfunctioning the fridge doesn't recognise that door is closed, because of that alarm sounds and light keeps on.
Check as well the freezer temperature if it is ok. If the rest of fridge functions are fine I would concentrate on the door switch.
Let me know how it goes.