[adtechperson]

I have worked for a number of ad tech companies over the years.

If this really is happening (and it seems possible it could be coincidence) the most likely explanation is cross device targeting using IP address.

So, most ad tech companies do cross device targeting, using device maps bought from other companies (Drawbridge being one). These companies attempt to assign a variety of devices from the same person to a single advertising profile. The simplest way they do this is by IP address. So if they have an IP address with a small number of devices, they decide it is probably a household and assign all those devices to the same advertising profile.

So, by being on the same wifi together (either at your place or hers) they will show ads on her devices based on your behavior (and vice versa).

The other explanations are possible, but I think this is the most likely

[patcheudor]

This is the correct answer. We noticed this happening in our small lab and decided to run some tests and in fact if one person searched for something odd like 'Swedish fish' then visited sites selling Swedish fish, everyone in the lab would start to get ads for candy and snack food. Similarly, searching for "mountain bike" would result in everyone else seeing ads for bikes and bike accessories. It sort of became a game to figure out what the test search term of the day was.

[otakucode]

Many would probably hear of experiences like that and think 'hey that sounds unintentional or like behavior the advertiser wouldn't want' but it actually sounds brilliant from a pure effectiveness point of view. You don't just show an ad to an interested person.... you increase the chance that the person will hear about the thing from people in their immediate vicinity. And what's the best advertising in the universe that no one can buy? Word of mouth.

Advertisers had better be paying through the nose for this sort of access, because it's insanely valuable.

[jackgolding]

We get this all the time in our office for salesforce (half of our team uses it.)

[justboxing]

Since this seems to be the most accepted answer, I did some search on IP address re-targeting, and came across this, which is kind of creepy and annoying.

> Cookie-based retargeting uses online data while IP Targeting uses offline data, which is verified and drastically reduces the potential of non-human bot traffic. IP Targeting essentially takes the traditional direct mail approach and matches home and business postal addresses to computer/device IP addresses.

Source: http://www.accudata.com/why-ip-targeting-takes-the-cake/

[idunno246]

its also more than just ip address. if you ever log into each others computers to check mail or any other system that requires a login, that company can sell your (device,username) pair to these cross device companies, and and you get another (device2,username) pair and its decided to be the same person.

https://whotracks.me/trackers/liveramp.html: twitch, okcupid, adobe

https://whotracks.me/trackers/drawbridge.html: etsy, aol, samsung

log into one of those from two devices and anyone who wants to pay will track you as the same person

[dogma1138]

I wonder if agencies register the GPS coordinates of open houses for location based advertisement.

https://www.tamoco.com/blog/location-based-marketing-history

[philwelch]

That has some super creepy implications--imagine the father of a teenage girl wondering why he's suddenly seeing so many internet ads for maternity products, for instance.

[dogma1138]

How Target Figured Out A Teen Girl Was Pregnant Before Her Father Did:

https://www.forbes.com/sites/kashmirhill/2012/02/16/how-targ...

[jackgolding]

Great story but apparently its a hoax:

https://www.kdnuggets.com/2014/05/target-predict-teen-pregna...

[vokep]

Can't find it atm but there was at least one story of someone being outed as gay due to ad targeting. For things like that, if you can think of it it probably already has happened, and if it hasn't, it will in the next 10 years.

[TYPE_FASTER]

Makes sense, especially since I think the IP for multiple devices on a home broadband connection would be the external IP of the broadband router, right?

[untog]

Correct. About the only solution is for everyone to have an independent VPN connection.

[asadlionpk]

VPN that anonymizes IP and isn't 1-to-1 mapped to person/device. Tor network?

[janesvilleseo]

I believe Google does this for suggested search. I’ve noticed that my suggested search is eerily spot on for my current conversation with someone who is searching or just searched for something that I too am now searching for.

[sfifs]

Yes. This is retargeting based on a cross device graph and this experience illustrates ad tech trade-off. We're those ads in a logged-in ad platform like Facebook or were they generic display stuff?

[PragmaticPost]

Well there goes Christmas shopping.

[eip]

> they will show ads on her devices based on your behavior (and vice versa).

She went house hunting and watched kung fu movies. Has nothing to do with the partners behavior.

Most android (CIAlphabet) phones have CIABook installed by default and it cannot be turned off or deleted without root access. Both listen to microphone and probably take random photos. The phones are both linked to credit cards which are probably also linked to Netflix account.

Why are people still surprised by this?

[raintrees]

I cannot attest to the above suggestion that "CIABook" is installed, as I have not reviewed any of the Android source.

Instead, I offer different information: I know of a person who is switching back to a pager to avoid smart device-based tracking. This after he received the requested "all information Facebook has about me" and saw how many of the quizzes he took for fun were advertiser-based, articles that seemed to be interesting (and were not about products or services, per se) being brought to his attention by advertisers, as well as other behavior he thought was innocuous but instead resulted in yet more data gathered about him.

It is my understanding he is piecing together different services to allow the pager to still be able to communicate (eventually) via IM with the right hand-offs involving services who rank privacy/no-tracking towards the top of their service offering.

There is some interest among his peers to offer this as a service, for those who might find this idea desirable. Apparently there are refurbished pagers available for purchase that can be used in this way.

He has jokingly referred to it as a "Hi-Tech detox" process...

[adamrezich]

I, too, listen to this person in the morning! Maybe attitudes have changed over the years but IIRC his partner isn't very well liked around here.

[raintrees]

I find thinking dimensionally helps me understand better...

[adamrezich]

I find HN to be a really interesting intersection point of the Dimensions