MERRILLVILLE, Ind. (WOWO) – Two elderly people were found dead in a northwestern Indiana home from suspected carbon monoxide poisoning after bird nests apparently clogged an air exhaust pipe, authorities said Monday.

A relative called 911 Sunday morning after discovering the two residents unconscious in the home in Merrillville.

Carbon monoxide is a toxic, odorless gas that is produced by combustion. It can be found in fumes produced by automobiles, generators, gas ranges and heating systems.

The Merrillville Fire Department reminds residents of the importance of having working carbon monoxide and smoke detectors inside their homes and also having their heating system inspected at least once a year.

The names and ages of the two dead people were not available Monday. Autopsies were scheduled to be performed Tuesday by the Lake County Coroner’s Office.