Yet another bomb threat at a Long Island school prompted an evacuation Friday, leaving some parents and students frustrated. However, police say they have to take every threat seriously even though it may cost manpower.

Police searched West Babylon High School after receiving word of the threat, but found nothing.

?They're getting tired of bomb scares,? West Babylon graduate Chris Morfesi says. ?I think it's four in the past seven days, it's kind of bad.?

The school superintendent says they've added extra hall monitors and are restricting student?s movements in the building, something that?s also been done in other schools.

At North Babylon High School, students? backpacks were searched as they entered school two weeks ago after a bomb threat. Miller Place High School seniors aren?t allowed to leave campus for lunch. That school is also monitoring when students leave their classrooms.

Suffolk police say the false threats are costing them precious manpower. ?It's very substantial, detectives are involved, forensics are involved, our patrol officers have to respond, so it's not a minor detail,? Suffolk County Police Commissioner Richard Dormer says.