Smoke Detector Placement and Wiring in an up-down Duplex

[Brad McGuirk]

I am currently rewiring a duplex I just bought and wanted some feedback on this:

I'm putting smoke detectors in each unit, should they all be connected? Or should each unit have it's own circuit?

If there are all one one circuit, technically it's a no go because one tenant is paying the electric for all the alarms.

I was thinking of wiring each unit on a separate circuit and linking both systems with a common wire so when one unit's go off, there other units go off as well, but the electric is still separate.

Am I looking into this too much? I may just contact the inspector as well.