How store anti-theft alarms work: Magnetostriction (2015) | Hacker News Reader

How store anti-theft alarms work: Magnetostriction (2015)

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56 pointspxndxx23 comments

Perhaps OT, but I have an Implantable cardioverter-defibrillator (ICD) [0] which zaps my heart if I experience cardiac arrest due to ventricular fibrillation, hopefully avoiding sudden cardiac death. I'm not supposed to linger in the vicinity of store anti-theft alarms as their magnetic fields can stop the ICD from correctly sensing (induction hobs do the same thing). In the worst case they can apparently cause the ICD to factory-reset, and emit annoying buzzing noises from inside my body. Ho hum.

[Edit] also, you should avoid ICDs if you are tin-foil-hat paranoid. Mine comes with a bedside telemetry monitor that reads data from the ICD every day and occasionally uploads it to the NHS mothership. The device-monitor RF protocol is proprietary and unpublished and the monitor has it's own 4G dongle.

[0] https://en.wikipedia.org/wiki/Implantable_cardioverter-defib...

May be OT or not but interesting nonetheless!

'KineticLensman', is this of the directed energetic chemical decomposition variety?

> 'KineticLensman', is this of the directed energetic chemical decomposition variety?

Ha!

Actually, since you ask, the ICD delivers enough energy to launch a tomato 40m into the air (assuming I have done my unit conversions correctly, and ignoring the effects of air resistance).

whoa! that's a kick to the ticker.

Yup, a very good friend of mine had one. He described the event as being kicked directly in the chest by a strong horse, completely by surprise (he'd grown up around horses and had a good idea of what a horse could do).

He was on a bit of a crusade to have the mfgr implement a pre-shock warning feature, just a buzz/beep/chirp/whatever a couple of seconds before triggering so he could prepare himself, as he'd found the shocks much more tolerable when he had an inkling they were coming.

AFAIK they haven't yet implemented it.

Since I couldn't resist: 40m is 29m/s at start; accelerating 0.15 kg tomato to 29 m/s requires 63J energy. Using that energy to heat tomato would heat it for 0.1 C (assuming that tomato is water).

> requires 63J

Pretty close. The actual device is 40J. Perhaps I should have specified the mass of the tomato a bit more accurately. (I was thinking more like .1 Kg)

Perhaps more OT but the back to base dialing of a pacemaker was part of the plot of a Columbo episode - "Blueprint for murder", hopefully haven't given too much away.

Great, I was planning on watching that exact episode today, you’ve ruined it for me. (J/k)

This is waaay OffTopic - but is a bugbear of mine

"""The device-monitor RF protocol is proprietary and unpublished and the monitor has it's own 4G dongle."""

1. All code funded by public money (NHS) should be FOSS by default. (I bet "security" has been mentioned in this defence)

2. My father had a similar device, and while he had an extra decade, I would far rather trust (his/my) life to open, reviewed code than what some person in some possibly dysfunctional company thought was best.

Anyway, I hope you don't set off any store alarms (yes my electronics groking might not be accurate) All the best.

So NHS should refuse to purchase best in category devices if the manufacturer doesn't want to deal with "FOSS"?

I guess FOSS advocates have a different definition of "best".

I assume they meant code directly funded (i.e. written by a subsidiary of) the NHS, not proprietary purchases. Seems that's not the case here though, the device is proprietary.

See my comment above. The NHS are implanting devices / software created by an American company, and use the supplied telemetry systems to get medical data. I have no evidence that the data is also sent back to the US company, especially given that the NHS are paying for the bandwidth.

This is (imo) the same debate as funding for science. Yes, big pharma seems to show you can have privately funded science - but this is a small corner case for science as a whole, and they still make their work public - its just copyrighted.

Imagine a pharma company announcing a brand new cure for "baldness" - but people would have to sign NDAs, could not remove their hats in public and so on.

They should use their purchasing power to force companies into having better software.

Have you ever seen good software written by a hardware company?

"Deal with FOSS" is an interesting way of phrasing "Not keep secret how an implanted medical device works".

There should be a fundamental right for patients to know this, otherwise they effectively don't have bodily autonomy.

Outside of emergency scenarios, they can forgo the treatments they don't feel are well enough explained, so I'm not sure "don't have" is entirely accurate.

Voting with their feet/wallet/choice of medical procedure? We have rights and regulations because these individualist methods have again and again been proven ineffective.

They had bodily autonomy at the time they made the decision. They gave it up in exchange for receiving the treatment, and thus no longer have it; the "don't have bodily autonomy" phrasing is accurate. The fact that this was a voluntary decision which they were perfectly entitled to make does not mean that it wouldn't have been better if they had another option which allowed them to receive the treatment without giving up their autonomy.

Merely not being provided with documentation for how the device works and how to control it I could overlook; after all, we don't even have that for the bodies we're born with. Everything we know about how we work is reverse engineered. But the patient is most likely prohibited by law from reverse engineering or otherwise tampering with this device which is now part of their body, and that I cannot condone.

> All code funded by public money (NHS)

The device is an Ellipse VR [0] produced by Abbott (formally St Jude Medical), and was not developed by the NHS.

> All the best.

Thank you, much appreciated.

[0] https://www.cardiovascular.abbott/us/en/hcp/products/cardiac...

The 4g dongle is so the device can be issued to people who don't have the means / skills to hook it up to wifi.

This reminds me that once where was a store I visited pretty often, almost every single time I entered the store, I would most likely trigger the alarm and nope, I did not carry such tags. The culprit seemed to be the credit cards in my wallet. This article seems to be able the explain what happened. I have to admit the design was both genius and dumb. It's simple, cheap and works most of time but can also easily by passed folding or removing the tag itself altogether. Most annoyingly, high false alarm rate.

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