The lights in cars can be a very frustrating experience for users. Most of us who drive have left our lights on and quite a few of us will have come to our cars to find them completely unusable for their primary purpose because of something we hardly realised we did.

In the UK, the major breakdown cover agencies report that they attend 10000s or 100000s of incidents a year where the problem is caused by a flat battery due to lights being left on.

Of course, there are safety concerns: hazard lights must always function indefinitely; and any electronic system must never switch off headlights ...

What would be an absolutely foolproof way of solving this problem without effecting the safety concerns associated with lights being able to stay on indefinitely ?

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    – Kit Grose
    Commented Dec 6, 2013 at 0:41

11 Answers 11


My previous car (a Volvo) seemed to solve this problem very well:

You turn the car off and the lights turn off automatically. If you need the lights on, you leave the key in position I or II (Intermediate/Accessory and Drive positions). If you have the keys on your person, your car's lights are off.

  • 1
    How do you leave the car parked with sidelights on? Commented Jul 5, 2013 at 7:57
  • 2
    Subaru does this as well (or at least they did years ago). The headlights are always off when the car is off, regardless of the position of the switch. This does not affect the hazard lights or map lights inside the car, however.
    – quietmint
    Commented Jul 7, 2013 at 15:43
  • 4
    @AndrewLeach You just have another button - just in case you want to keep the lights on all the time. Otherwise, they turn off automatically
    – Oleg
    Commented Jul 8, 2013 at 6:25
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    +1. The default should be easy, and the exception discoverable.
    – MSalters
    Commented Jul 8, 2013 at 14:55
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    The problem with this kind of non- standard arrangement is when someone doesn't read the manual/ loses the manual. GM cars used to have a totally obscure method of turning the cabin lights on.
    – PhillipW
    Commented Jul 12, 2013 at 7:44

I think that wouldn't it make more sense to partition the battery such that even if the lights are left on, by the time they die, that the car still has enough reserve charge to start. This still follows your requirement that the lights must not be switched off by any electronic system as the lights only die when they use up the charge in the partition of the battery from which they are allowed to draw.

  • I just remember that some luxury cars actually have two batteries and use them as I have described.
    – Dan D.
    Commented Jul 5, 2013 at 2:19
  • Canal boats use this system, with the batteries used to power internal electricity (lights and sockets in the living area) separate to the battery used for engine ignition.
    – TRiG
    Commented Jul 5, 2013 at 15:07

You say "any electronic system must never switch off headlights", but there are a few cars that have automatic mode for headlights. The cars have a photocell somewhere to detect brightness, and will toggle the headlights accordingly. They typically have a feature that when the driver leaves the car, the lights will remain on for 30 seconds or so, before turning off automatically.

An automatic mode deals with the UX issue you mentioned, and also has the added bonus of the user not having to remember to turn on lights when driving -- that's also a safety bonus.

Another simple solution is to create a second electrical circuit and power source which is responsible for starting the engine. This way the lights can drain one power source, but you always have a backup mechanism to start the engine and charge up again with the alternator.

  • 2
    The user should still have the ability to turn lights off manually. One of my cars does not allow this, and it is a problem for me because I regularly use a car ferry. They request drivers turn off their headlights but I am unable to do so. The problem with automatic lights is there are legitimate reasons a user would want to choose differently than the sensor. Therefore an override is needed which puts you back at square one Commented Jul 6, 2013 at 15:15
  • Most cars with an automatic option also have the other options - off, on, fog, etc. But yes, once you switch to "on" or "fog" you are back in the situation of possibly leaving your headlights on.
    – elemjay19
    Commented Jul 11, 2013 at 22:33

Car makers have developed various systems to reduce the risk: Beeps when you open the driver's door with the lights on, beeps and alarms when you try to lock the car with the lights on or a door open, inner light switching off after some time or when the keys are out of range.

One important detail is even though such systems exist since a long time, not all cars are fitted with them, for cost/marketing reasons. For example, entry-level compact cars sometimes have no central locking, no remote keyless ignition system and just a basic on/off switch for inner lights. This could account for some of the reported cases.

  • My car beeps when I open the driver's door with the lights on. Great until the fuse controlling the beep goes.
    – Urbycoz
    Commented Jul 30, 2013 at 8:42

Have your car send a message to your phone X minutes after it has been locked if any lights are on...

Could also send a message if battery drops below X% ...

  • This would require the car to have a cellular/internet connection. Do you have an example of a system which does this, would be interesting.
    – rk.
    Commented Jul 7, 2013 at 3:08
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    @rk: It's a concept but if you Google I'm sure you can find options (e.g. text2car.com ). Also see lockitron.com .
    – Guy Sirton
    Commented Jul 7, 2013 at 3:29
  • The Tesla Model S already has the internet connection, and may do this...You can also turn the lights on/off from your smartphone. Commented Jul 8, 2013 at 12:47
  • I think this kind of thing will come quite soon - there's some pretty smart tech going into cars now: readwrite.com/2012/04/02/…
    – PhillipW
    Commented Jul 8, 2013 at 17:17
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    BEEP-BEEP, "Hey, Michael, you left my lights on again..." Commented Jul 10, 2013 at 5:48

Some other solutions:

  • Leave the lights on for a short time after the car is parked (configurable, usually in the 30 seconds to 2 minutes range). This helps with the use case where the driver uses the lights to find their front door. I've seen this on many high-end cars.
  • If the driver has overridden the normal behavior (say by flipping the Subaru switch to leave the marker lights on), then turn the lights off before power gets low enough that the car wouldn't start. I would expect cars as smart as the Tesla to do this if there were no other solution. In the Tesla's case, it could also call/text/email you, and/or alert Tesla HQ if power were getting low.

Summarizing other answers, it's a simple solution. The lights are completely automatic:

  • They turn on when it's dark
  • They turn off when it's day
  • There's a way to force the lights to be on during the day (some states require lights when it's raining)
  • They turn off when the car is off (after a delay so you can have light when getting into your home)
  • The only way to keep the lights on is with the key in the ignition
  • The hazard lights can still be on without the key in the ignition

With everything automatic, the driver doesn't have to think about ever turning them on or off. This has been a solved problem for some time, but several car makers have failed to get on board.

  • Actually the above does not solve the problem. At least every time my battery has drained, it's been the following scenario: 1. Night time, lights are on automatically. 2. Give car to valet, who parks car, turns off ignition. 3. Valet, not knowing lights will turn on when the ignition key is turned, turns lights to forced on position on starting car. 4. I drive home, turn off car and walk away, thinking headlights, which are on, will turn off as usual in a few seconds. 5. Lights stay on all night. 6. Call valet company in the morning and complain while I wait for AAA to arrive. Commented May 10, 2016 at 23:55
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    @EricStoltz, take a look at bullet five: "the only way to keep the lights on is with the key in the ignition"
    – Chris Calo
    Commented May 28, 2016 at 17:05

The solution has been around for a while: If you leave the lights on and turn the ignition off the car beeps at me and the badly translated French on the display says “Lights not on?”

(And I think there's some override button combination should you actually want to leave the lights on.)

  • true, but with my car, this only happens with the headlights
    – Toni Leigh
    Commented Jul 4, 2013 at 21:25
  • Sidelights on mine as well.
    – PhillipW
    Commented Jul 4, 2013 at 21:27
  • internal light ? boot light ? both of which often remain on if the doors aren't properly closed
    – Toni Leigh
    Commented Jul 4, 2013 at 21:28
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    My current car beeps if key is out and driver door opens. My old car didn't beep, but once when I left the lights on, my neighbour called me and said "your headlights are on". So either beeping, or having friendly neighbours prevent leaving lights on for too long ;)
    – Samuel M
    Commented Jul 5, 2013 at 5:30
  • Friendly neighbours are certainly a win, but a little hard to spec. out for a car manufacturer !
    – Toni Leigh
    Commented Jul 5, 2013 at 7:24

Car lights on? Check 1.

Engine off? Check 2.

Driver's door open? Check 3.

3 checks = BEEP.

The beep will indicate that something is 'wrong', and so the driver will check to find the source.


My Honda Insight beeps when you leave the car lights on. Which helps, but man, so much beeping in the world today, its practically background noise. Like thousands of other people yesterday, I left the lights on and needed a jump in the morning.

Baffled at how a car that can stop and start the engine at a stop sign, can't detect the combination of ignition off and lights on and battery about to go flat. You're gonna lose the lights eventually, so not sure there is any thing safer than checking those three variables and killing the lights before the battery doesn't have enough charge to start the engine.

I know this is not a luxury car but, you'd think that would be a standard thing for Hondas.


Well I think Peugeot figured it some years ago without adding extras (auto lights are still an extra this days) When the car is turned on you can turn your lights on too, however, once you turn off the car the lights turn off (leaving the lights switch in ON position), however if you turn off and on the lights again, you override the auto off mode, so you can have you lights turned on without the key and even locking the vehicle. Of course, if you don't override the auto off function, the next time you ignite the car, the lights will be turned on unless you switch them off.

Edit: I've just realized this question was made back in 2013, I'm a little late, however I consider this still relevant.

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