The desperate Munich man even did gymnastic exercises while trapped on the second-floor balcony on Wednesday in an effort to keep warm - in between trying to persuade his two-year-old grandson to open the door.
"I don't understand why he didn't shout out for help, into the street or courtyard or something. I'm sure I would be shouting a lot if I were stuck out in the cold for that long," a spokesman for the city's fire department told The Local.
"We are not sure whether the little boy thought he was playing a game, or whether he was unable to open the door," he said.
"The man was only wearing slippers and the kind of clothes you wear around the house. He had only popped out onto the balcony to smoke a cigarette. But he was on the second floor, six or seven metres up off the ground, so jumping down was not an option."
The grandfather, who was only babysitting the boy while his parents were out, eventually managed to get the toddler to pass him a phone through the window which was tipped open - and he called the parents.
But when they returned home to rescue him, they found the door key was stuck in the lock from the inside - and had to call the fire brigade to let them back in.