Why are websites requesting access to motion sensors... on my desktop?


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I was checking the status of a FedEx order in Brave, when I noticed a notification in the address bar that I've never seen before. It was warning me that "this site has been blocked from accessing your motion sensors". Wut? It doesn't even need to be an order status - their home page kicks it up too.

I'm struggling to understand why a website would need access to a motion sensor on a mobile device, let alone the fact I was using a desktop. Do I get a different experience if I knock my PC off the desk? Tip my monitor on its side? Grab the mouse cord and spin it around my head really fast?

After a few cursory online searches, I'm coming up with little other than a few threads on Reddit and Brave that indicate people are also seeing this on Kayo Sports and Twitch, as well as Experian and Tutanota.

Guess it's time to dig a little deeper.

What are Web APIs?

Before zeroing in on sensors, let's backup a sec and talk about web design and Web APIs. Your browser has access to a lot of data via (and metadata regarding) the device you installed it on. As much as some of the websites you visit would looove to have access to all that data, any decent browser acts as a firewall, blocking that access by default and prompting you to allow it.

Geolocation API

One of the more common APIs is the one used to request your location, usually when you're using a websites's "store locator" to find the store nearest you.

The button below uses code (lightly modified) from MDN's Geolocation API docs. When you click it, the JavaScript code executes a call to navigator.geolocation.getCurrentPosition(), asking the browser for your location.


Your browser prompts you to allow access, which you can deny. Yay privacy.

If you don't see the prompt but you think you've allowed it, there are two different settings that control access - a global page with a list of "blocked" and "allowed" sites, and a per-site page where you can adjust all permissions for a single site. In Chrome, just replace brave:// with chrome:// in the address bar.

Notifications API

Another (unfortunately, very) popular API is the one used to display notifications to visitors. Using the Notifications API, you can request permission from a visitor with a call to Notification.requestPermission() and then just create a new Notification() to annoy them keep them up to date. (May not work in Brave due to a bug.)

Sensors API

There's a (maybe sorta?) new API for requesting access to sensors in Chromium-based browsers (Ghacks puts it at Chrome 75, around June 2019, but wikipedia suggests Chrome 67 around May 2018). It's not widely supported yet. According to MDN, the only major browsers that currently support it are Chrome and Opera, on desktop and mobile.

Check out the MDN docs, the W3C candidate recommendation, the ongoing conversation over at Chrome, and Intel's Sensor API playground for examples.

The following links execute some JavaScript code to try starting up various sensors, which should trigger the sensor icon in the address bar. (If an error occurs, it'll display below the links.)

Status Message: N/A

As with the geolocation and notification APIs, you can grant or deny access at the global or per-site level. What's kind of annoying is that all of the above sensors fall under a single "motion sensors" umbrella, so you can't easily tell which of those sensors a particular site is trying to access.

Why are certain sites requesting the Sensors API?

That's the hundred-dollar question. I see it on FedEx and Kayo Sports (every time) and Twitch (sometimes). I'm sure there's other sites too, but the question is, why do sites as varied as these want access to a gyroscope or accelerometer?

I haven't confirmed anything, but if I had to guess, I'd say they're all using the same library, and it got changed. Like all modern development, websites are built upon layers and layers of libraries that depend on other libraries. Somewhere down the line, I wonder if one is requesting access to an API that it doesn't need? After poking around a bit, I didn't see anything obvious, but then some of the scripts were obfuscated so there's little chance of figuring those out.

Your guess is as good as mine, but like all the Web APIs, if you don't believe a site needs the data it's requesting access to, tell your browser to block it!


Grant Winney

Is there anything more satisfying than sharing knowledge? Of teaching someone and witnessing their "ah ha" moment? I hope you found something here today that led to your very own "ah ha" moment! 💡