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Comment by derefr | Hacker News Reader

In what way are watches with SIMs (or eSIMs) not just tiny cell phones? Or is you meaning that the modern smartphone is itself a “pile of hacks sitting on top of hacks”?

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The main way is that literally zero of these watches actually meet the standards that the cell networks require of a cell phone. Every single one of them has a carrier exemption or a lower standard to adhere to, because it turns out that putting a cell phone's RF package into a watch is super hard, both because of size and the various negative effects of the human body on radio signals. This affects cell phones too of course, but less so (remember the iPhone 4 and how we were "holding it wrong"?).

Another way is that watch chipsets are distinct from cell phone chipsets in that they make a variety of compromises unique to wearable requirements. Apple may be an exception here, you can't get a spec sheet for their chip, but for the other providers their wearable chipsets are generations behind anything they sell for a cell phone and are compromised in terms of power. Interestingly even watches (Apple, Samsung soon) that support 5G are running a dumbed down version of 5G that was created specifically to support the wearables and IoT market.

It gets even stranger in software. A text showing up on your watch might have arrived two completely different ways depending on whether it's an iMessage or a regular text and you can't tell which. The watch often doesn't even have its own number -- it's borrowing your phone's. IOW, it's not a tiny phone doing phone things, it's a companion device trying to fake it.

A few years ago, I signed up for an Apple Watch eSIM plan (which is a special type of eSIM plan that Apple make cell carriers agree to offer as an add-on to a normal cell subscription for your iPhone, and there is no other way go get an eSIM for it).

I then started regularly receiving phone calls (to my iPhone) intended for someone else. At first I thought it was a wrong number or an old number and kept telling them to remove this number. Buy the calls kept coming and I eventually I dared to ask what number they had dialed. And it wasn't a cell number I recognised.

After contacting support for my carrier, what I figured out was that the Apple Watch eSIM has its own phone number, for some reason, but it's not one you're supposed to know about; as an extension of your phone's subscription, the Apple Watch eSIM notionally has the same number as it. But they were calling the secret number associated with the eSIM, somehow. And I think there was a problem in the number routing table somewhere, because I think this number may have been in use with another cell carrier, and the calls only went to me when calling from my network?

Absurd nightmare situation.

Or opportunity for fun

Surprises you didn't give that secret number out - could have been fun for yourself (or your close friends or family) to be able to call direct.

I wonder if you could even use it for texts or notifications that only go to the watch ?

the Apple Watch eSIM has its own phone number, for some reason, but it's not one you're supposed to know about

Not a secret if you have AT&T. The watch and its phone number are listed right there in its own section on the bill.

Absurd nightmare situation.

Not unique to Apple Watches, or any other device.

I have a T-Mobile hotspot that was assigned a recycled phone number. It gets several text message receipts each day for someone's Venmo purchases.

> two completely different ways depending on whether it's an iMessage or a regular text

Isn't that true for any device? not just watches?

A "regular text" would be an SMS and those use Signaling System Number 7 telephony stack.

iMessage uses application level protocols sitting on top of IP in the standard OSI model?.

SS No 7 only roughly maps into OSI model, the equivalent application layer would use MAP - Mobile application part.

> SS No 7 only roughly maps into OSI model, the equivalent application layer would use MAP - Mobile application part.

Well yeah only the OSI stack actually maps onto the OSI model, or should be expected to

What do you mean by "carrier exception"? Exception from policies those same carriers set up decades ago?

Not exactly. Early cell watches were not going to meet the existing carrier standards and so they received specific exemptions from the carrier to operate on their network. Over the years the carriers have created requirements that are specifically for these devices, that are less stringent than what they require for a cell phone on their network. They still give specific exemptions if a watch is "close" to meeting a requirement but can't quite get there.

Restricting users to "approved" devices seems to be a US thing? I'm fairly sure that anything that's capable of connecting with the right frequencies and protocols can connect to any UK network.

This isn’t the case for these watches in the UK as well, as they only work on certain partner networks, but I’m unsure whether this is due to the GP claim or something else.

That seems more likely to be due to the device being network locked, rather than the networks disallowing them?

Can't quite speak for UK, but in EU cases I know about its because some (popular) watches need special provisioning process for eSIMs and getting that proprietary software requires carrier to beg our favorite mega corps for provisioning software and do extra work.

It's not like phones where pSIMs were relatively brand agnostic, were back to per-hardware BS.

I have a Pixel Watch 2, it seems that only certain carriers (typically not MVNOs) can set it up with an eSIM that will present as having the same number, but any MVNO that provides eSIM setup via QR code should work to provision via the connected phone.

I can imagine Apple being less inclined to allow arbitrary eSIMs on their watches, preferring to only support the case where the eSIM is guaranteed to support the "correct" presentation.

So yeah, "standards" they themselves set up which decimated market competition on US markets.

How nice of them to make an exception.

> various negative effects of the human body on radio signals

I was under the impression radio waves couldn’t interact with biological matter in any meaningful way. Can you share more about this?

The body both absorbs RF, meaning there has to be a safe absorption rate (SAR) and creates impedance with it. It also creates radio shadows. What’s more, larger individuals have more of this effect. At Fitbit there was a guy who I’ll refer to only by his first name — Tim — who was our first port of call for whether or not our prototypes were getting the job done, RF-wise. He was a very large human. (proportionally speaking — he was also very fit!)

I've found my calling. Is this "Tim" role open now that he's left?

Fitbit is owned by Google now — are you sure you want that job? ;)

Radio waves are not ionizing radiation, so they aren't directly cancerous in the same way as say, x-rays or UV light (UV light is about the threshold for this), but they are still absorbed by water in tissue, which heats it up slightly. There is a limit to how much this is safe, and so radio safety standards impose limits on the average power you can use to transmit in most consumer devices. The standards are stricter for something intended to be carried in a pocket or worn on the body.

You get far more of a heating effect from just standing in the sun.

I was under the impression radio waves couldn’t interact with biological matter in any meaningful way.

You don't have a microwave oven?

Matter of any kind interacts with radio wave on some level. You might be thinking of how radio waves in the bands and power used for cellular don't have a negative health impact. But they still 100% interact and the human body, being both dense and conductive, absorbs radio waves beautifully.

Of course they interact, but to my knowledge this interaction is not meaningful when discussing biological functions.

I think you may have switched the "of" and "on" when you read the original post. They're saying that the human body can negatively affect radio waves, not that radio waves have a negative effect on the human body.

As others have said, but also the Apple "watch shares your phone number but not really" where you have a second "real" phone number that actually communicates - reminiscent of how Republic Wireless worked on the Sprint network.

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