# No mechanical car door key. Battery dead as a doornail. How open door? **URL:** \ **Category:** Factual Questions\ **Created:** [September 2, 2013, 1:54pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798 "2013-09-02T13:54:22Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [September 2, 2013, 5:21pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/21 "2013-09-02T17:21:31Z")
Rick, see PM if you have a minute. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 2, 2013, 5:40pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/22 "2013-09-02T17:40:22Z")
> [@Johnny\_L.A](#): > > **Rick** : Are you thinking of the 5150 police code? 'Cause that’s what it means to me. 🙂 5150 a danger to themselves or others. You would be amazed at the stupidity of some drivers. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [September 2, 2013, 6:03pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/23 "2013-09-02T18:03:28Z")
> [@rsat3acr](#): > > if a kid is inside and can’t open it from inside, you break a window. Using, as your tool, the head of the dealer who sold you this car. Or your own head, for being stupid enough to buy such a car. (If, in fact, breaking a window is what it takes.) Or the head of the engineers who designed such a car. I’ve wondered similar things myself, and I would hesitate to buy a newer car without checking out questions like this. (And, I admit I haven’t read all the posts in this thread yet to see if there’s actually an answer.) But I’ve certainly read plenty of horror stories of various sorts related to these electronic access systems. Okay, now I’ll read this thread. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 2, 2013, 6:39pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/24 "2013-09-02T18:39:05Z")
> [@Senegoid](#): > > Using, as your tool, the head of the dealer who sold you this car. Or your own head, for being stupid enough to buy such a car. (If, in fact, breaking a window is what it takes.) Or the head of the engineers who designed such a car. > > I’ve wondered similar things myself, and I would hesitate to buy a newer car without checking out questions like this. (And, I admit I haven’t read all the posts in this thread yet to see if there’s actually an answer.) But I’ve certainly read plenty of horror stories of various sorts related to these electronic access systems. > > Okay, now I’ll read this thread. Before you go for the head of the dealer, how about you fire up that third brain cell and THINK for about 10 seconds and you will realize just how stupid and far fetched this scenario is. First off you are telling me that the battery was fine and unlocked the car just fine, you put the kid in the car closed the door and the battery had plenty of power to re-lock the car (at this point regardless of anything else you are no longer in the running for parent of the year) and then magically instantly the battery goes dead? I have never seen this in over 40 years in the auto repair business. In other words not gonna happen. Next assuming the child isn’t an infant how about you ask them to pull the inner door handle and umm open the door? Boy that was tough. Fact is you are far more likely to lock your traditional key in the car than you are to lock a proximity key in the car. Like I said 5150. ---
**Author:** ![Digital\_is\_the\_new\_Analog](https://avatars.discourse-cdn.com/v4/letter/d/a88e4f/32.png) [@Digital\_is\_the\_new\_Analog](https://boards.straightdope.com/u/Digital_is_the_new_Analog)\ **Post date:** [September 2, 2013, 7:03pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/25 "2013-09-02T19:03:12Z")
> [@ombre12](#): > > I doubted a microchip would have enough power. I know it is enough to retain an odometer reading, but that would take very little power. You’re still mixing the controller and the power source. The typical use of the word microchip has absolutely no power. It needs power from something else - a battery of some sort in this case - so it can think. It’s job is to take inputs to react to the outside world - a key turn, an RF signal of a key nearby - and drive outputs to cause something to happen - turn a motor on to mechanically unlock the door. Think of it this way. Take your standard digital watch. Take the battery out. It still have a microchip in it, but it isn’t telling time anymore because it has no power. > [@Leo\_Bloom](#): > > Good pick-up line. You’d think so, right? Been using it for years, and still single! ☹ 🙂 ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [September 2, 2013, 7:07pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/26 "2013-09-02T19:07:13Z")
> [@ombre12](#): > > It is hard to actually talk to a mechanic at a dealership and the salesmen will tell you the first thing that pops into their minds. I see you’ve fixed the problem, but this response is just nonsense. ---
**Author:** ![48Willys](https://avatars.discourse-cdn.com/v4/letter/4/db5fbb/32.png) [@48Willys](https://boards.straightdope.com/u/48Willys)\ **Post date:** [September 3, 2013, 5:47am UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/27 "2013-09-03T05:47:54Z")
> [@](#): > > Originally Posted by ombre12 View Post > It is hard to actually talk to a mechanic at a dealership and the salesmen will tell you the first thing that pops into their minds. > [@](#): > > Originally Posted by Chefguy View Post > I see you’ve fixed the problem, but this response is just nonsense. Maybe where you live, But for those of us in the rest of the USA, Salesmen will say ANYTHING. In my experience, service managers will seldom let you talk to an actual mechanic. The service manager may or may not be a mechanic. Is there grease under his/her fingernails? If not they are probably not real a mechanic. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [September 3, 2013, 8:01pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/28 "2013-09-03T20:01:46Z")
> [@48Willys](#): > > Maybe where you live, But for those of us in the rest of the USA, Salesmen will say ANYTHING. > > In my experience, service managers will seldom let you talk to an actual mechanic. The service manager may or may not be a mechanic. Is there grease under his/her fingernails? If not they are probably not real a mechanic. There is a very valid reason for that. I pay my technicians to repair cars not answer questions. Answering question for people that are too lazy to RTFM belongs to (pick one) the salesman, service advisor or me the service manager. FTR even my dumbest salesman knows the answer to this question. ---
**Author:** ![ombre12](https://avatars.discourse-cdn.com/v4/letter/o/d26b3c/32.png) [@ombre12](https://boards.straightdope.com/u/ombre12)\ **Post date:** [September 3, 2013, 8:10pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/29 "2013-09-03T20:10:00Z")
> [@Digital\_is\_the\_new\_Analog](#): > > You’re still mixing the controller and the power source. The typical use of the word microchip has absolutely no power. It needs power from something else - a battery of some sort in this case - so it can think. It’s job is to take inputs to react to the outside world - a key turn, an RF signal of a key nearby - and drive outputs to cause something to happen - turn a motor on to mechanically unlock the door. > > Think of it this way. Take your standard digital watch. Take the battery out. It still have a microchip in it, but it isn’t telling time anymore because it has no power. > > You’d think so, right? Been using it for years, and still single! ☹ > 🙂 Now I am real confused… So how does a digital odometer keep its memory for days weeks or months (maybe years) with a dead or disconnected battery? I figured it was some kind of micro chip. If not that, what? ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [September 3, 2013, 8:16pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/30 "2013-09-03T20:16:04Z")
> [@Rick](#): > > FTR even my dumbest salesman knows the answer to this question. This reminds me of a story I heard once: Some guy was giving Charlie Watts the business and Mick says, “Hey! Leave my drummer alone!” Charlie shoots back with, “I’m not his drummer! He’s _my_ singer!” ---
**Author:** ![ombre12](https://avatars.discourse-cdn.com/v4/letter/o/d26b3c/32.png) [@ombre12](https://boards.straightdope.com/u/ombre12)\ **Post date:** [September 3, 2013, 8:20pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/31 "2013-09-03T20:20:01Z")
> [@Senegoid](#): > > Using, as your tool, the head of the dealer who sold you this car. Or your own head, for being stupid enough to buy such a car. (If, in fact, breaking a window is what it takes.) Or the head of the engineers who designed such a car. > > I’ve wondered similar things myself, and I would hesitate to buy a newer car without checking out questions like this. (And, I admit I haven’t read all the posts in this thread yet to see if there’s actually an answer.) But I’ve certainly read plenty of horror stories of various sorts related to these electronic access systems. > > Okay, now I’ll read this thread. Well it doesn’t pertain to the Lincoln I was posting about…that was just not paying enough attention on my part the first time I looked at it. My bad It does seem to pertain to some BMW’s with battery under hood and no mechanical way to open a locked car door (except for opening the trunk, tapping into the trunk light with a portable jump box or jumper cable) I was wrong about Lincoln but what was BMW thinking? ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [September 3, 2013, 8:25pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/32 "2013-09-03T20:25:24Z")
> [@ombre12](#): > > Now I am real confused… > > So how does a digital odometer keep its memory for days weeks or months (maybe years) with a dead or disconnected battery? I figured it was some kind of micro chip. > > If not that, what? You can store information in memory, like your camera stores images on the memory card. That requires no power and will last effectively as long as we want to store information. But it doesn’t store power and it can’t do any work. If you want power to do work (such as open a door lock) you’ll need either a capacitor or battery in the system. ---
**Author:** ![ombre12](https://avatars.discourse-cdn.com/v4/letter/o/d26b3c/32.png) [@ombre12](https://boards.straightdope.com/u/ombre12)\ **Post date:** [September 3, 2013, 8:29pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/33 "2013-09-03T20:29:12Z")
Makes more sense now Thanks. ---
**Author:** ![ombre12](https://avatars.discourse-cdn.com/v4/letter/o/d26b3c/32.png) [@ombre12](https://boards.straightdope.com/u/ombre12)\ **Post date:** [September 3, 2013, 8:35pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/34 "2013-09-03T20:35:00Z")
> [@ombre12](#): > > Makes more sense now Thanks. Come to think of it although most of my electronic stuff wii lose their memory if power goes out and no back up battery… But my DVR will keep all of its memory if power goes out. A lot of memory there too and no back up battery. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [September 3, 2013, 8:40pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/35 "2013-09-03T20:40:39Z")
> [@ombre12](#): > > It does seem to pertain to some BMW’s with battery under hood and no mechanical way to open a locked car door (except for opening the trunk, tapping into the trunk light with a portable jump box or jumper cable) A quick search online shows that there is a mechanical way to open the locks using the key when the battery is dead, but it’s just not very well known. Or the mechanical key mechanism is in a poor state from not being used. I haven’t looked at the newest models but all the ones I’ve seen with a quick search online have a physical key as well as keyless entry. Can you show an image of a BMW with no physical key? ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [September 3, 2013, 8:42pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/36 "2013-09-03T20:42:33Z")
> [@ombre12](#): > > But my DVR will keep all of its memory if power goes out. A lot of memory there too and no back up battery. Your DVR is saving to a hard disk drive or solid state memory which don’t require power for long term storage. There are other forms of volatile memory which get reset when they lose power but are more suited for some applications. ---
**Author:** ![Raza](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/raza/32/213_2.png) [@Raza](https://boards.straightdope.com/u/Raza)\ **Post date:** [September 3, 2013, 8:55pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/37 "2013-09-03T20:55:27Z")
IIRC from my 2005 Corvette, there is a cable in the trunk (not exactly a trunk, since it was the coupe model, so more like a hatchback) that you could pull that would unlock the driver door. Not an electrical cable, a hardwired heavy-duty cable. The '05 had a “feature” where if you didn’t leave it in reverse (stick shift), the dash stayed illuminated. I drained my battery three times over my 2-year ownership. ---
**Author:** ![TerpBE](https://avatars.discourse-cdn.com/v4/letter/t/bc8723/32.png) [@TerpBE](https://boards.straightdope.com/u/TerpBE)\ **Post date:** [September 3, 2013, 9:02pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/38 "2013-09-03T21:02:10Z")
I once parked my car next to a curb that was so high I couldn’t open my door, so I had to climb out the passenger’s door. It was only after I returned to the car that I realized there was no keyhole in the passenger door, and my power locks didn’t work. D’oh! Luckily I was able to get the driver’s door open 3-4 inches and use an umbrella to manually unlock the passenger door. ---
**Author:** ![ombre12](https://avatars.discourse-cdn.com/v4/letter/o/d26b3c/32.png) [@ombre12](https://boards.straightdope.com/u/ombre12)\ **Post date:** [September 3, 2013, 10:13pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/39 "2013-09-03T22:13:33Z")
> [@Telemark](#): > > A quick search online shows that there is a mechanical way to open the locks using the key when the battery is dead, but it’s just not very well known. Or the mechanical key mechanism is in a poor state from not being used. I haven’t looked at the newest models but all the ones I’ve seen with a quick search online have a physical key as well as keyless entry. Can you show an image of a BMW with no physical key? It wasn’t me. I got it from a link on post #4. Just trusted that link was being accurate about BMW’s ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [September 3, 2013, 10:19pm UTC](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798/40 "2013-09-03T22:19:27Z")
> [@ombre12](#): > > I was wrong about Lincoln but what was BMW thinking? Whatever BMW was thinking is magnitudes better than Lincoln. Best damn cars I’ve ever owned. [Previous page](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798.md?page=1) [Next page](https://boards.straightdope.com/t/no-mechanical-car-door-key-battery-dead-as-a-doornail-how-open-door/667798.md?page=3)