The warning system was tested at Towantic Power Plant in Oxford on Wednesday morning.
Alarms and intercom evacuation notices sounded around 9 a.m. The noises shook residents and Connecticut State Police said they got several phone calls concerned about it.
Connecticut State Police said there is no threat at this time of the warning.
Police said the public was not warned about the test and town officials confirmed that they did not receive any notification of the test on Wednesday morning.
"We regret that advance notice was not given to the town of Oxford about the brief testing at the CPV Towantic Energy Center this morning. We did inform the local first responders immediately following the test, but are committed to providing notification in advance moving forward," Competitive Power Ventures, Inc., who manages the Towanic Power Plant, said in a statement on Wednesday.
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