Five grenades were found near the house of a retired Army officer at Belthangady about 60 km from Mangalore, the police said on Sunday.
In his complaint to the police, Jayakumar Poojary, said he noticed the grenades near a barbed wire fence while he was walking down the mud track towards his house.
While four grenades were found scattered, one grenade was in a yellow plastic cover. The grenades carry a manufacturing date of 1979-80.
The ex-Army officer later kept the grenades at a "safe place" near his house so that stray animals or children don't take them away, the official told the police.
Superintendent of Police Rishikesh Sonawane said the grenades appear to be 40 years old. The police are trying to find the source of these explosive substances. The Uppinangady police registered a case against unknown persons for offences under Sections 25, 1(B) and 7 of the Arms Act, according to a report in The Hindu.