 Emergency officials set to test the alert system of the Salem-Hope Creek nuclear power plants tonight. DEMA will set off the 37 sirens within 10 miles of the power plants, which includes Delaware City, Middletown, Odessa, and Townsend. Residents hearing the sirens, which will last three to five minutes, are advised to tune to WDEL for a message in case of an emergency. The sirens are tested four times a year.