How do I keep from leaving a car in idle overnight?

You turn the key off and remove it. Take it with you when you get out of the car, lock the car and walk away. Done.

If you have keyless ignition, press the start/stop button to turn it off. Get out. Lock the car and walk away. Done, again.

And before you do either of these, make sure the parking brake is on.

You may have half-heard and completely misunderstood people taking about accidentally leaving a stereo or the like on all night. That would only happen if it was badly installed and not wired through the ignition key/lock. Turn it off, if this is you.

You turn the key off and remove it. You can not remove it if the engine is still running. It is not hard to do at all. key out engine id OFF!

Just follow the correct turning off procedure when leaving the vehicle after a while it becomes so automatic you will never make that mistake.

Which basically you can make even by mistake.

unless you have a car made at the start of the Twentieth Century not Twenty first Century !

Besides which keyless cars shut down when the chip controller is far enough away from the car.

And those with a key .The key can not be removed with out shutting down/Turning off the engine

For you since your understanding is so confused, check the exhaust pipe before you go away from the car. If exhaust is coming out and you can see it flutter a business card held up to it. If you're still confused raise the hood and see if the pulleys and belts are standing still. No exhaust means the engine is not running. No pulleys turning or belts moving means the engine is off. For the rest of us in the civilized world, put the key in your pocket and notice the dash lights are all out.

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Just read an article about a guy who died in his sleep after his Toyota kept running all night in the attached garage. If your question is "howcome..." the answer is "'cause that's how it is". Give him his "Darwin Award".

The dealer should have a re-flash to change how the car works. Look up the recall or TSB. I'm not going to do that, since it's somebody else's problem not mine.

remove the key. car will be off.

The key comes out of the ignition switch when it's in the off position.

what about cars with keyless ignition? No key to remove. Never owned a car with keyless ignition or even driven one so have no idea how it works.

You can't remove the key unless it is in the Off position.

'Idle' is when the car is sitting in neutral or park with the engine running. Only idiots leave a car in idle overnight, and it's sheer luck that the car isn't either stolen - because it can't idle without the key in the switch - or the engine blowing up or the car catching fire.

You always remove the key. You can't remove the key and have the car still be running.

You don't leave a car 'on battery'. You can leave the lights in the 'on' position and drain the battery. You can also run the battery down by leaving the key in the switch in the position where the radio and other powered items will function. Sitting in the car for awhile after you get home, listening to the radio with the engine off, can drain the battery to where the car won't start.

If you pull out the key, the engine has stopped running. The car cannot run without the key inserted unless you have one of those keyless cars but even then I think it automatically shuts off if the key is too far away.

If the car has daylight running lights then look at the headlights. If it’s on, motor still running.

You can feel a little vibration when the motor is running unless you have one of those energy efficient cars where the engine shuts off when the car comes to a stop.