HARRISBURG – Three Mile Island will begin to test a new emergency siren system. The first test is scheduled for 12:30 p.m. today and will last for three minutes. Power plant owner Exelon says the sirens have improved sound and better battery backup to ensure they’ll work during an electrical outage. Ninety-six sirens are scattered throughout communities within a 10-mile radius of the plant. Three more tests are planned through mid-November. Sixteen sirens in Lancaster County did not sound during a test last year due to a timing glitch, which was later remedied.