If your grandparents live in a house, give them gifts, for example soot gas sensor. Carbon monoxide can be life-threatening.
The soot gas sensor has been mandatory in all homes with fireplaces since the new year, and they may not have been aware of it.
Also, be cute and help them put it in the right place, because the sensor on the cabinet is of no use.
And if you're already in the village this Christmas, check it out smoke detectors, because they have a fixed period of validity, they may have already expired.