Interrelated smoke alarms - are they necessary?

[Sara Abernethy]

I'm doing a knob & tube re-wire because after years of handymen messing with it, I want to make the house safe for my tenants. I'm getting quotes now, and the electricians have been suggesting interrelated smoke alarms. This makes sense to me because the last few sets of tenants have taken the smoke alarms down - which infuriates me, but they don't care and they do it anyway. (I rent a 4BR single family home to college age and early 20-somethings. They're usually unrelated. The building is 3 floors.). 

Has anyone had issues with hard-wired smoke alarms? While it sounds safe, it also sounds harder to troubleshoot. When a smoke alarm keeps beeping for no reason, you can just take the batteries out. One of the electricians is telling me that it's not necessary to have hard-wired smoke detectors in SFH in Philadelphia, while the others are strongly recommending it.