Three members of a family, including a man, his wife and their son, were found dead inside their house in Chennai's Mettukulam near Koyambedu after they inhaled poisonous gas from an air conditioner, said the police.
The victims have been identified as Saravan, 35, Kalaiarasi, 30, and Karthikeyan, 8, the police added.
According to the police, the family went off to sleep while the inverter for their AC remained switched on after a power cut in the evening. When the power restored later, it caused the AC's cylinder to emanate toxic gas, which lead to the family suffocating to death since no doors nor windows were open, according to the police.
Bodies of three persons have been sent to the Government Kilpauk Medical College Hospital for post mortem.
An FIR has been registered for further investigation, they said.