BEDFORD, Texas (CBSDFW.COM) – The city of Bedford confirms outdoor warning sirens have gone off two nights in a row.

The emergency warning sirens sounded in the northwest part of the city without anyone activating them.

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The city says its system was not hacked and they are trying to figure out what caused the sirens to go off.

Meantime, the cities of DeSoto and Lancaster are still working to upgrade their siren network after leaders there said their systems were hacked.

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The sirens went off in the middle of the night last week.

Those sirens remain disabled for now.

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The cities have also brought in federal investigators to try to find whomever was responsible.