How does a "smart" key know the keys are not inside the car

I carpooled last night with a friend who has a car that doesn’t require putting a key in to start the car. She was explaining how great it was because she never takes her keys out of her purse anymore. She said the car can sense when the keys are near, so she just pushes a little button on the door handle and it unlocks it, then when she returns to the car, she pushes the button to unlock it.

So it occurred to me—does the lock/unlock button work if the keys are left INSIDE the car? It seems it would have to know they were outside or the likelihood of accidentally leaving your keys inside the car would be a problem.

Am I right that the car must know that the keys are outside? And if so, how does that technology work?

From wiki:

What you’re describing is called a prox key.

Different models have different features (such as, I used to have a VW that would not let me lock the driver’s door while it was open). However, I’m willing to bet that 99% of cars with prox keys don’t care if it’s inside or outside. If the key is within range, the lock/unlock buttons are active. So, yes, you could lock your keys inside but this isn’t really a problem because you could just push the button to unlock it again.

The only problem I can see is that if you left the key inside the car (perhaps in a the pocket of a jacket which you took off?) then a would-be thief could simply enter your car and drive away.

The potential for theft is exactly what I was getting at. So it DOES allow you to lock your keys inside the car? We’ve had a rash of crime in our area where thieves are just walking down the street and trying every parked car to see which ones are unlocked, then when they get lucky they take anything of value.

With this new smart key system, they could do the same thing by trying the little button to see if anyone has left their keys in the car.

I’m guessing a hide-a-key would be a bad idea with this type of car.

But someone else told me today that on their car, that feature only works if the keys are OUTSIDE of the car. If that is true, I’m hoping someone will chime in here and explain how that works.

Seems like a carjackers dream. Pull up in your bmw to a red light and the guy unlocks your door and gets you

I have a BMW with the “keyless” feature. It will not let me lock the keys in the car. Og help me, I’ve “tried” it more than once. The keys need to be very close to the car for the locks to disengage when you’re outside. If I need to unlock from farther away, I use the buttons on the fob. Also, once the car has started with one set of keys, you have to physically hold the second controlling key up to a certain spot on the steering wheel to switch control from one key to another. I occasionally care about this when my husband and I are carpooling and the car sensed his keys first.

The locks will likely behave differently depending on whether the engine is running or not - for example, I can’t open my trunk using the button on my proximity fob if the car is idling.

My car - Lexus is250 - will not let me lock the keys in the car.
It will beep furiously if I try, and won’t lock the doors.

I suspect it uses a simple heuristic - if it can see the keys inside the car via one of the transceivers inside, and it can’t see the key next to the door handle transceiver, it refuses to lock.
The door and boot (trunk) transceivers let you open the car or boot keylessly when outside the car. Overall the system works rather well.

Because the car is littered with transceivers, it is possible to implement fairly smart rules. Once the car is running the rules on door locking change anyway.

A friend of mine has an Audi, and it let her lock the keys in her car. When she explained to the Audi agent that she had just bought a couple of kilos of fish, which were also inside the car, they quickly agreed that they would waive their usual “we will come and fetch it on a truck and fix it next week” to - “OK will will break a window and repair that next week.”

A lot of cars auto lock the doors when put in drive. Unless you put the car in park at red lights a would be thief couldn’t open the door.

My car will not let me lock the keys inside. Once when we were out and I was driving, my wife wanted to leave her purse inside the car when we made a stop. The car kept yelling at us until we figured out that her key inside her purse was the cause.

Just to second what others have said, I can’t lock my key inside my car (2016 Accord, but my 13 accord wouldn’t do it either). I also couldn’t lock it in my trunk either. If I tried, the trunk would just pop right back open. That causes a (small) issue if you try to close the trunk the with key too close. I’ve heard reports of women pushing the trunk lid down with their purse and having it open back up.

I have theories on how it works, but I’m not sure. FTR, I’ve never tired, say, putting the key in the back seat and locking the door to see if that works.

One thing that bugs me with this, and it may be Honda specific, is that I can’t lock the doors, with the key outside the vehicle and the car running. For example, If I want to keep the car running and run in to the gas station or store my options are lock the doors OR leave the engine running. I’m not sure why it can’t be both. My understanding (though I’ve never tried it) is that if the car is running and the key is in it, is that the engine will cut out if you put it in gear without the key inside the car.

Also, just FTR, if I get out with the engine running (and my key is always in my pocket), the car beeps at me. It’s very aware of where the key is at any given time.

I’m kind of curious as to what would happen if I tossed the key out the window while I was driving. A FOAF had his Proximity motorcycle key bounce out of his saddle bag while he was riding on the freeway. He had to go back and try to find it after the engine quit.

And while we’re here, I want to mention that I LOVE my smart key. I love not having to dig around for keys (it’s the only one I carry). In winter I just bury it deep in an inside pocket in my jacket and all I ever have to do is push buttons. It’s a nice convenience.

(insert my “This is progress?” schick here)

Can I start the car, turn on the heater and fan, close the door and load the baggage in the trunk?

Will it refuse to open the trunk while the engine (ICE for a bit yet) is running?

This is a ritual I remember from childhood in snow country - Dad would volunteer to “warm up the car” before the woman and children entered. This was also the time when stuff got loaded into the trunk.
Did we just lose this?

(why yes, I Do have no experience with the technology. thank you for noticing)

Can you explain to me like I am a first grader how the car knows that the keys are outside? That is incredible imo. People are genius!!!

(quote=joey pOne thing that bugs me with this, and it may be Honda specific, is that I can’t lock the doors, with the key outside the vehicle and the car running. For example, If I want to keep the car running and run in to the gas station or store my options are lock the doors OR leave the engine running. I’m not sure why it can’t be both. My understanding (though I’ve never tried it) is that if the car is running and the key is in it, is that the engine will cut out if you put it in gear without the key insi

Serious First World Problems :wink:


Explain like you are a 1st grader? Hmmmmm…lemme try.

The key shines an invisible light that is “seen” by the many “eyes” that are placed at various places on the car. Depending on which eye sees the key, or which eye sees the key first will allow the car to determine where the key is in relation to the car.

Yes to all the sensible things. The car will beep at you when you are close by with the key when it is running, but everything continues to work. Mine stops beeping when you get too far away (like going back into the house) but the car stays running. (I have the opposite but allied need - when it is 45 C outside having the aircon run is vital.) Most cars have a remote boot opener in the cabin anyway. Cars tend to try to behave safely, and will err on the side of not doing something stupid rather than behave ultra secure.

Yes, you can start the car, get out and leave it running. As I mentioned before (at least with Honda vehicles), you just can’t lock the doors in that scenario, but the car can be running without the key inside the car. It’s only necessary to be in there to start it.

Also, yes, you can open the trunk (with the button on the trunk) when the car is running. But since you can’t lock the doors with car running AND you can open the truck when the car is unlocked w/o the key nearby, that may be moot. However, it wouldn’t surprise me if the programming exists in the computer so if there’s ever some kind of software upgrade to allow the doors to be locked with the engine running, that feature is already tested and ‘working’. It wouldn’t even need to be turned on. But that’s just a guess.

Serious First World Problems :wink:

Not directed at you, specifically, but I hate it when people say that. Just because someone exists in a third world county that barely has enough to exist, doesn’t mean I shouldn’t be able to mention that I don’t like a feature on my car or that my coupons didn’t work at the store or that there’s a scratch on my phone. I understand the sentiment, but if my phone wasn’t scratched or my coupons redeemed properly or the feature in my car worked the way I wanted it to, the person in the third world county would still have third work problems.

Recently, I have been having a problem with my coupons not redeeming properly at my supermarket. I was moaning about it at work and and all the BS hoops I’ve been jumping through in an attempt to get it cleared up. Someone muttered that it’s a ‘rich people problem’. F-that. As I said to him 'I’m losing out on about $150 a year in coupons, are you saying you wouldn’t fire off a few emails to try and get it cleared up, I don’t care if you make $10k or 50k, that’s a lot of money" Oddly enough, he said he wouldn’t. Which seemed odd, as someone that works under me, the $150/year represents a much more significant amount of money to him than to me.

Like I said, I understand it, it just bugs me because it doesn’t make sense. It’s like when I was younger and wouldn’t finish my lunch and someone would say ‘ya know, there’s starting kids in Africa’. I always used one of two ‘comebacks’. Either ‘if I finished this, they’d still be hungry’ or ‘feel free to pack up the leftovers and ship it to them’.

One problem that occurred to a friend of mine was not about locking the keys inside : Mom and Dad get into the car at point A. Dad is sure he has the key fob in his pocket, but the car is recognizing Mom’s fob in her purse, so the Start button on the dashboard works fine. Once they get to point B, Mom leaves the car (engine still running) and Dad continues alone to point C. Dad parks the car at point C and determines that he can’t find his fob… so he can’t restart the engine to go back to point B.

In more recent models, they’ve added a loud beep if the keys leave the car while the engine is running.

I’ve heard of people in situations like that ‘can you drop me off?’ They get into that person’s car, drop the person off, driver drives away with the car and can’t restart it later without the key. For example ‘can you drop me off (and pick me up later) at the bar/friends house/library etc?’.

I should check to see what happens if I try to put my car* in gear without the key in the car. ISTM it should kill the engine. Not only for this situation, but also to make sure it can’t get stolen if I get out with the engine running. IIRC, cars with with remote starters do this.

*My car is stick shift, but it could even be set to kill the engine if the brake is depressed so it’s the same on stick or automatic.

Love it!!!

Another Q:

For those who have their car and phone linked so that the phone can start the car (this is being done, right?):

What happens with phone lost/stolen? Can the finder/thief now steal your car?
I assume there is some easy way to disable the phone/car handshake. Just how big a window does the thief have?