Thieves stole the catalytic converter of our 1996 Mitsubishi last year. They can do this in ~1 minute and you don't realise it is missing until you start the motor and then you probably think something is broken instead it is missing.

Our car was very loud, we thought there might be a hole in the exhaust pipe. And the missing catalytic converter is indeed something like a hole. :-) And we don't use it daily, as the city I live in is very bike friendly. So our car can stand here a whole week without getting moved.

Fixing it cost us I think between 700 to 1000 EUR, and I think we were lucky at that time. Because it was one of the first of the cases in our area and we were lucky to find a used one.

If your exhaust line is cut, broken or just rusted to the point of having holes, the sound of it will change, but also the exhaust gases won't come out from the back of the car but in the middle under it, and go inside the cabin very easily, you'll be able to smell it, and this might get seriously dangerous to inhale if you try to drive

You would notice as soon as you turned on your car. It would sound like a roaring sound from under your car and would get worse any time you give the engine more fuel. You can drive a car without a catalytic converter but it is almost universally illegal and you assuredly won't pass emissions.

removing the catalytic converter essentially renders your muffler useless since it's located in the middle of the exhaust pipe [0]. therefore removing the cat. converter will make your car incredibly loud and virtually impossible to go unrecognized.

[0] https://media.hswstatic.com/eyJidWNrZXQiOiJjb250ZW50Lmhzd3N0...