
Ask HN: How is tracking done across devices? - oretoz
I was watching a movie called Pad Man on Netflix App on my Amazon Stick. The movie was about sanitary napkins. When I opened a webpage (on procrastination which was on the top page of HN yesterday) on my iPhone, I was shown an ad about sanitary napkins.<p>I don’t think it is a coincidence but I am keen to understand how such user tracking works.
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davismwfl
In general, every time you buy something or browse a site where you have
logged in on multiple devices your user agent details are stored for each
device (and generally sold). There is an inherent uniqueness to much of the UA
details stored. That combined with your browsing habits allows companies to
collect this data from multiple sources and then resell it as targeted ad
marketing. So if you use multiple devices they can still track and target you
as a person instead of a device. The advantage of this method and others like
it, is there is no dependency on cookies or other things that can cause cross
site issues. Content providers use this data to advertise you things which you
might have an interest on based on content you have consumed, hence your
sanitary napkins ad.

You can check out companies like Geocommerce, they do location based
targeting, but also follow the user from device to device.

There are other methods as well, just giving you one data point. My knowledge
comes from having done it, and yes I glossed over a lot of the details.

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dangerface
Some other methods to fingerprint a device:

TCP Headers SSL Cookies language headers fonts

Different browsers will render the same page in different ways which results
in resources being loaded differently, you can detect this. They will also
send different headers for different types of content, for example a picture
could be byte served html generally isn't.

You can easily detect if its a mobile device and then ignore ip but instead
track an ip range.

There are lots more ways to track a device online without cookies or IP, its
fairly easy. The devices are often connected by sharing a login or an ip if
both are on your wifi. Once the connection is made between devices its never
forgotten.

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yuhong
I mentioned that in my essay/overview BTW.

