(Londonderry Twp.) -- New emergency warning sirens will be tested in the ten-mile zone surrounding the Three Mile Island nuclear power plant. On Monday, crews will begin the process of checking the 96 new sirens that were installed beginning in October. The new emergency warning devices have battery back-up power and cost about $2.8 million to install. The sirens will go off for 30 to 60 second durations and will sound similar to the machines they replaced.