From what I can see there are three sensors... (1) at the exhaust manifold passenger side, (2) just after the front cat on the drivers side (3) just after the front cat on the passenger side... The other two rear cats are sensor free...

Lots of 02 sensors... One would think they would sound the alarm if the cats were gutted... Granted it's illegal to remove catalytic converters for a street licensed car... And rumor has it, removing them won't improve HP unless they are clogged and obstructing the exhaust flow... Which is highly unlikely for cars that are only a few years old...

So, the question still stands... And this is a loaded question...