The 63-year-old man's housemates heard a loud boom from the back bedroom, then followed the noise to find the man had been shot in the head.
Detroit police are trying to discern where that bullet came from and who fired the shot.
The shooting took place before 6:40 a.m. Tuesday on Detroit's west side, said Dontae Freeman, social media manager for the Detroit Police Department. This was on the 12600 block of Mendota, which is north of Grand River and east of Meyers.
The two people in the house with the victim called police after finding him suffering from the head wound. Medics transported the victim to an area hospital, where he is in critical condition.
Police at the scene found glass fragments on the floor and windowsill, but no shell casings inside the room, and are investigating the shooting.