FAIRFIELD — Students and staff at Lawrence High School and the adjacent junior high were placed on lockdown Tuesday before authorities determined an alarm had been mistakenly activated.

“An accidental activation of the system” prompted the security measure, which lasted about an hour in the morning, according to Fairfield police spokesman Officer Casey Dugas.

He said there was no danger to people on campus and that it was “determined a false alarm pretty quickly.”

Authorities searched the school complex before the lockdown was lifted.

Fairfield police in a Facebook post commended the school staff for “their professionalism in an unknown situation.”

It wasn’t clear how the alarm was mistakenly activated.