K-9 cars are partitioned off.

The dog rides in the back, separated from the front seat.

THat is too keep the dog inside the car should the cop have to exit car quickly- often dogs will key in on adrenaline or the excitement of the handler-
So, if an handler jumps out of the car the dog won't jump out into traffic or start a chase on their own.

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K-9 units have a screen between the back seat and on the rear windows in some commmunities. THey usually have a huge k-9 sticker on the rear door and some kind of "Don't stick you hand inside" warning on there too.