Sirens meant to warn thousands of people of any emergency at a nuclear plant complex north of New York City stood useless for nearly six hours Tuesday when power was lost to a signal transmitter and the failure went undiscovered.

There was no emergency, and the 156 sirens were not needed during the outage. But "the bottom line is it's inexcusable," said Larry Gottlieb, a spokesman for Indian Point owner Entergy Nuclear Northeast (search). "That system should never be down for any time."

Gottlieb said the cause of the outage was not known but there was "no evidence of sabotage."

Entergy and the Nuclear Regulatory Commission (search) were investigating the failure.

Westchester County Executive Andrew Spano, who has been demanding a backup power system for the sirens, said he would ask the Federal Emergency Management Agency (search) to investigate as well.

The sirens, in suburban Westchester, Putnam, Rockland and Orange counties, are meant to alert residents within 10 miles of the complex to tune in broadcasts about any emergency.

"The public was never in danger," Gottlieb said. He said that if an emergency had occurred the failure of the sirens would have been noticed and a battery would have been brought in to activate them.