# Does the car battery interrogation method work in reality? **URL:** \ **Category:** Factual Questions\ **Created:** [January 15, 2023, 1:27pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257 "2023-01-15T13:27:15Z")\ **Posts on this page:** 17\ **Page:** 3
**Author:** ![Lare](https://avatars.discourse-cdn.com/v4/letter/l/53a042/32.png) [@Lare](https://boards.straightdope.com/u/Lare)\ **Post date:** [January 19, 2023, 11:55pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/41 "2023-01-19T23:55:50Z")
> [@Great\_Antibob](#): > > While directly across the heart may be difficult, it should be possible to deliberately drive enough current using a car battery to lock up your heart but realistically only if you placed the electrodes under the skin on top of really cranking that battery. Of course, it isn’t really torture (from the OP) if you’re using the voltage across b the heart. You won’t get much information from the dead subject. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [January 20, 2023, 8:54am UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/42 "2023-01-20T08:54:15Z")
And I think we all agree that while torture is ineffective as a means of gaining information, it can work (to quote Candide) pour encourager les autres. ---
**Author:** ![Fridgemagnet](https://avatars.discourse-cdn.com/v4/letter/f/22d042/32.png) [@Fridgemagnet](https://boards.straightdope.com/u/Fridgemagnet)\ **Post date:** [October 13, 2023, 9:53am UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/43 "2023-10-13T09:53:13Z")
> [@mixdenny](#): > > The only time I have ever felt 12 volts was when i was working on a horn circuit and got buzzed. The horn has a big coil that turns on and off to vibrate a diaphragm. Somehow it can shock you also. Perhaps the collapsing field is more then 12 volts? This happened to a friend of mine when we were kids - he was messing around with a motorbike battery and a horn, and was surprised to get a shock when he disconnected the wires. “But it’s only 12 volts, how can I get a shock off that!”. It mystified me too for years, until I grew up to be an electronic designer and learned about inductance: the horn coil has a sizeable inductance (L), and when the horn circuit is broken the rate of current fall (di/dt) will be quite large, so the inductive kickback voltage (V) will also be large as V = L(di/dt). It’s the same reason one often sees sparks inside a light switch when turned off - inductive kickback from the wiring. > [@Al128](#): > > And yes, having people hold spark-plugs is an old mechanics-joke … you get a good jolt but given that it is just a split second - there is no real harm. Back in the old days of points and ignition coils, maybe (but even then it was Russian roulette as an unlucky jolt could still stop your heart), but modern ignition systems have a much higher energy HT output, and a greatly increased risk of instant death. Additionally, running a modern ignition system without a spark plug connected to each HT lead can easily blow up the ignition module, so instant death _and_ a broken car. Double bummer. ---
**Author:** ![Al128](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/al128/32/16541_2.png) [@Al128](https://boards.straightdope.com/u/Al128)\ **Post date:** [October 13, 2023, 5:17pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/44 "2023-10-13T17:17:49Z")
duly noted … I shall refrain from asking my girls from testing for spark with their tongue 🤪 just out of interest: from a conceptual POV, is there a difference between the voltage feed to a spark-plug compared to an electric fence? … → high voltage jolt for a split second, right? ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [October 13, 2023, 6:14pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/45 "2023-10-13T18:14:58Z")
> [@Crafter\_Man](#): > > A hundred AAA batteries in series could kill you. When I was in grad school, the storage room of our research facility had a battery on the shelf, maybe the size of two iphones stacked together. It was labeled as 300 volts, and I assume it was intended as some kind of super-steady reference voltage for research instrumentation. It was pretty old (and that was 30 years ago), and I never saw anyone use it. Turns out something similar is available today: > **[Amazon.com: Exell Battery 493A 300V Alkaline Fits Replaces Eveready ANSI 722,...](https://www.amazon.com/Exell-Battery-493-Alkaline-Orange/dp/B00OKNPDM8)** > > EXCELL BATTERY 493A Battery Alkaline 300V Not sure what kind of current it can deliver across a human body, but I’d wager this might actually be dangerous. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [October 13, 2023, 6:30pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/46 "2023-10-13T18:30:17Z")
The method works fine for interrogation if you know how it works, and the villain doesn’t. Take a pair of jumper cables, tell the villain you are about to attach them to certain sensitive parts of their body, rub the ends to generate some loud and clear sparks. The villain will talk rather than find out what actually happens when you attach the clamps as you have suggested. ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [October 13, 2023, 6:33pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/47 "2023-10-13T18:33:55Z")
Probably not. That’s not a lot of voltage and your skin has a really high resistance. Even tying a hundred AAA is probably more dangerous from individual cells overheating and popping (relatively high internal resistance) than from the risk of electrocution This 300V battery would be more dangerous as a large-ish blunt object to bash over one’s head ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [October 13, 2023, 7:03pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/48 "2023-10-13T19:03:21Z")
> [@Great\_Antibob](#): > > This 300V battery would be more dangerous as a large-ish blunt object to bash over one’s head It only weighs one pound. A hammer would be better. I strongly disagree that this battery can’t bite you. It is rated for 25mA continuous current. Put a couple in series and you are in the 500VDC danger zone. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [October 13, 2023, 7:32pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/49 "2023-10-13T19:32:24Z")
I was working on a phone line when someone called which is 90VAC. Skin was dry but I definitely felt it. Very uncomfortable and I see how that could be used in the right way as torture device. “Tell me Mr. Bond. Should I phone a friend?” ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 13, 2023, 7:38pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/50 "2023-10-13T19:38:25Z")
Household current is 120V, and that can do some serious damage, so I imagine 300V could, too. Household current is probably more dangerous, despite the lower voltage, because AC of around that frequency has a tendency to fibrilate the heart, but it can also just plain cook you. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [October 13, 2023, 8:19pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/51 "2023-10-13T20:19:48Z")
50 volts is generally the highest voltage that is considered “safe”, though I’m sure someone at some point has figured out how to kill themselves with it. Industrial control voltages tend to run at either 24 or 48 volts. You need at least 24 volts so that relay contacts will be “self cleaning” (the arc from the contacts closing will punch through any arc residue or light corrosion), and anything under 50 volts is generally safe to touch. 100 volts and above is definitely not safe to touch. > [@Great\_Antibob](#): > > That’s not a lot of voltage and your skin has a really high resistance. Your skin’s resistance isn’t a fixed value. It depends greatly on what is referred to as the “touch voltage”. At low voltages like what a multimeter uses to measure resistance, your skin can measure hundreds of thousands of ohms or more, and can easily get up into the mega-ohm range. Generally, the skin’s “resistance” drops as you increase the voltage, and once you get up around 500 volts it drops dramatically as that high of a voltage can effectively punch through the skin. The human body’s effective resistance at that point is down around 1,000 ohms, which is a significant drop from the value of up over a meg that you get from a multimeter. > [@Marvin\_the\_Martian](#): > > It is rated for 25mA continuous current. 5 mA is the maximum “safe” current, at least as far as most safety standards are concerned. 20 mA is high enough to prevent you from breathing, and could potentially cause your heart to go into fibrillation, though you really need to be up close to 100 mA to reliably screw up your heartbeat. > [@Saint\_Cad](#): > > I was working on a phone line when someone called which is 90VAC. Skin was dry but I definitely felt it. Ouch. Fortunately that 90 VAC is current limited. It has to be able to tolerate a dead short without damaging the phone company’s equipment. > [@Chronos](#): > > Household current is probably more dangerous Not only for the reasons that you stated, but according to a friend of mine who helped design circuitry for a doctor who was experimenting with early pacemakers way back when, right around 50 to 60 Hz or so is pretty much the ideal frequency for stopping your heart. When they were doing animal testing, they would use a 60 Hz shock to put the animal’s heart into fibrillation. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [October 13, 2023, 8:23pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/52 "2023-10-13T20:23:17Z")
When I was a kid in the 1970s I purchased a 67.5 V battery. I don’t remember why I bought it; I think I was building a tube radio, or something. Anyway, I could definitely feel the current when I touched the terminals with my fingers. I just did a Google search. Interestingly, [you can still buy this battery](https://www.google.com/search?q=67.5+V+battery). Not sure what it’s used for nowadays. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [October 13, 2023, 8:31pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/53 "2023-10-13T20:31:53Z")
> [@Crafter\_Man](#): > > Not sure what it’s used for nowadays I was curious, so I went googling. Looks like it is very popular in radiation survey meters, along with several other 67.5V batteries in different form factors. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [October 14, 2023, 12:19am UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/54 "2023-10-14T00:19:11Z")
I recently got some high voltage generating modules like below. I’ve mostly been using a lithium 18650 cell and just touching the ends to the input wires. The arcs are very loud and startling. They’re super cheap and actually quite scary\*. A couple in series would make for a very intimidating interrogation enhancer and you’d still get to use the car battery and jumper cables. \*I was considering making a sparking cracking candy bowl for Halloween but, even if I could make it safe enough, I think it would be too scary for unsuspecting kids. > **[Amazon.com: DEVMO 5PCS DC 3v-6v to 400kV 400000V Boost Step-up Power Module...](https://www.amazon.com/DEVMO-400000V-Step-up-High-Voltage-Generator/dp/B07T3XDMH8)** > > description please notice: the high-voltage module should avoid the use of electricity in high voltage no-load . (Power must be adjusted to a suitable distance to the high-voltage output line , battery capacity is proportional to the distance and... ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [October 14, 2023, 12:25am UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/55 "2023-10-14T00:25:20Z")
> [@Saint\_Cad](#): > > I was working on a phone line when someone called which is 90VAC. Skin was dry but I definitely felt it. Very uncomfortable and I see how that could be used in the right way as torture device. “Tell me Mr. Bond. Should I phone a friend?” Reminds me of an old prank. You call up someone at home, explain that you’re with the phone company whose employees are working on the phone lines on a nearby telephone pole. You tell the homeowner that they shouldn’t use the phone for the next hour or so, as doing so would electrocute the worker on the pole. After a while, you call back the house and let it ring and ring. Eventually, the homeowner answers the phone, so you fake a bloodcurdling scream into the phone. Freak out the homeowner into thinking they’ve just killed a poor phone company employee. ---
**Author:** ![MikeF](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@MikeF](https://boards.straightdope.com/u/MikeF)\ **Post date:** [November 8, 2023, 10:51pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/56 "2023-11-08T22:51:31Z")
I remember touching the the spark plug lead as I pulled starter cord on a lawn mower. Don’t ask me “Why?”. I guess I thought it was loose or something. I was very young. Let me tell you, that was a hell of a shock. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [November 8, 2023, 11:24pm UTC](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257/57 "2023-11-08T23:24:22Z")
_NCIS_ in the _Legend_ Episode Depicted a guy strung up with copper wire coiled around his chest. A 12V battery near his feet. Dr Mallard said the current paralyzed the victim’s intercostal muscles and he eventually suffocated. That’s an example where low Voltage could be deadly. Assuming Ducky is right. I’ve been shocked pressing the kill tab against a mowers spark plug. It requires a firm press. I was 13 and a little scared. I was sweaty and hesitated. **Zap** It hurts! [Previous page](https://boards.straightdope.com/t/does-the-car-battery-interrogation-method-work-in-reality/978257.md?page=2)