Fire alarm need to be hardwired?

[Aref Shehadeh]

Rewiring most of a house I'm flipping due to it containing knob & tube. Taking down a load-bearing wall and redoing some of the ceiling on the first floor. The house was built in 1930. Fire code states if a house was built prior to 1976 it can have battery operated smoke detectors. New construction required hardwired or wireless interconnected systems. 

Does a rehab qualify as new construction in the eyes of fire code? Guess I'm asking if I can get away with just using battery smokes or would I need to upgrade the whole house. Going to call the fire department but wanted to extend the question here first.

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