We are all inter-connected.

Interconnected, hard-wired smoke detectors are another. 

We had to supply new fire extinguishers for all units & outside hallways, then install hard wired interconnected Smoke/CO detectors.

That's why many people opt for 3-units instead, where the fire alarms need to be interconnected but no panel is required.As @Robert Wodogaza said, it's certainly getting tougher to find good deals.

And each city is different with regards to their targets:  for example Farmers Branch and Hurst require hard-wired, interconnected smoke detectors; Lewisville does not. 

Do you have any feeling for if the interconnected utilities are a result of old SFHs being converted to small multis, rather than buildings that started as multis?  

Most of these units under permit will require electric service upgrades and rewiring, 20 amp gfi's new outlets/switches, interconnected smoke/carbon detectors ect which leads to opening a lot of walls, if these are plaster figure all new drywall.

@Nathan G. going to add to yours, top of window sill can be no higher than 44", the window must have at least 5.7 sq' glass, window well must be 9 sq' / 3' space in front of the window ( so a 3' x 3' window well is acceptable ), a ladder must be installed if the window well is deeper than 44" the second means of escape can be a basement door or cellar stairs that lead up and you are able to exit from that floor, door to the exterior must be 3' wide in the house to be acceptable for egress. ceiling height 7' min, smoke detectors in the hall and each bedroom ( check with town, they may want you to install hard wired interconnected smokes)

Some jurisdictions require the entire structure to be upgraded to interconnected smoke detectors if your are remodeling a certain percentage of the building.

What I've ran into most commonly is that any sort of remodeling work that requires permits will require that you also install hardwired, interconnected smoke/CO detectors throughout the property.