Google Knows Where You Sleep and What Your Walls are Made From

“The Tell-Tale Heart” is one of Edgar Allen Poe’s most well-known short stories, first published in 1843. In it, a crazed person kills an old man and hides his body in the floorboards. When the police arrive, there is no evidence to be found, and the murderer almost gets away – until the crescendoing thunder of a heartbeat brought on by his guilty hallucinations forces him onto his knees. He confesses to the officers and tells them where they can find the body.

A classic story. But in the future, it may need to be updated.

“How did you find the body, officers? There were no clues, there was nothing!”

“It was simple. We googled it.



Wait, Really?

Okay, this is obviously an exaggeration. The level of accuracy and precision this would take is well beyond anything going on right now by a very large degree.

But the idea that Google might know what’s in your walls – at least reasonably well – is a lot closer than you might think.

In a great post about a Google patent at one of my favorite blogs, SEO by the Sea, search marketing director Bill Slawski writes about the mapping of internal spaces:

The approach behind the patent is the following method.

(1) Identifying a map of an indoor space,

(2) Receiving inertial navigation signals (sensor signals from accelerometers, etc.) from a set of mobile devices moving through that indoor space and

(3) Calculating user trajectories based on the inertial navigation signals. This method provides direction and speed of movement of the mobile devices being tracked. Tracking these trajectories helps to identify walkable areas of the indoor space being targeted, and where turns take place among these paths. The inertial navigation signals (INS) may include: accelerometer data, gyroscope data, and compass data.

Google isn’t just tracking your phone’s position in your home. It’s tracking how fast it’s moving, how fast it’s speeding up or slowing down, what direction it’s pointing, the latitude, longitude, and altitude, how strong the wireless signal is, and anything else it can scrape out.


Like this, but in your pocket and always on.

Remote Wireless Domucartography

Let’s think about your different behavior in your different rooms, by time of day. Your bedroom is going to be the easiest to spot – it’s the room where your phone reports, “I’m plugged in, it’s 11pm, alarms are set, and I’m not being used for 8 hours.”

With a bit of fuzziness around the time to account for different people and different lifestyles, the bedroom may very well be the starting point of what I’m calling RWD – Remote Wireless Domucartography. (Domu from domus, “house” in Latin.)

We know some things about bedrooms, right? You and I? Let’s think about bedrooms. Bedrooms usually have one little room attached – a closet. That room doesn’t get much cell phone action. Some bedrooms may also have bathrooms attached, and bathrooms will, for short periods of time, get a lot of cell phone action. I mean c’mon, are you supposed to just sit there?

Bedrooms also connect to the main house, but they almost never have a door to the outside – unless, sometimes, it’s a deck above a lower level of the house. Thank goodness for that altimiter.

Based on these common things about bedrooms, I’d guess 90% of homes just got a little more mapped out. We can also use the total size of the home – something Google can ascertain through this data, or just by looking at Google Earth and guessing – to set some loose rules. For instance, if you have home small enough to be a studio, or large enough to be a mansion, some of these rules may not apply. A tiny studio will likely not have two bathrooms, while a mansion will have far more.

The other rooms, like kitchens, dining rooms, living rooms, dens, and whatever else, may be a little harder to differentiate. Google will know your wireless signal strength, however, and know that wireless access points are not likely to be stationed in the kitchen. And while you don’t often go into your dining room to grab something and then walk out right away, most people do this in their kitchens looking for food.


A heatmap of wifi signal strength.

(Image credit: Wireless Site Surveys. I gotta give BCI a free plug here – I’ve worked with them before and all my experiences have been excellent.)

I’d say it will still be pretty easy to determine the layout of the rest of your house, especially with a few more logical rules thrown in too. Google will know where your walls are because you’ll obviously never walk through them. It will compare this generated layout to the total frame of your home. Then, if there are any blank spaces, it will assume they’re support columns, rarely-used storage areas, boarded-up areas where you keep your dead bodies, that sort of thing.

So Google has a map of your house. And every other house on the block. And every other block in America. After some statistical modeling, it’s going to find there are only a few variations of most houses commonly built and get even better at using that data to model the rest.

Hell, with another year of exploring that data, Google’s algorithms might be able to design a better floorplan than architects.

But how is it going to find those dead bodies?

Waves All Around You

You may be aware that wireless technology is not black magic, but actually radio signals flying through the air all over the place – including in your walls, your floors, and even you. This is obvious; it’s not like you stop getting service if you turn your back on your router.

That being said, you do slow it down a little. Usually not enough to even notice. But your phone might.

Google is going to know right away where your router is. (I’m assuming for the rest of this article that, like most homes, your wireless router is also your one and only wireless access point.) It’s easy to tell, because it’s where your best service is.

If you’re walking away from your router, your service gets a little worse, every step. But if you suddenly place a wall between you and your router, the service gets even worse. Markedly, noticeably worse. Two walls, and it’s more than twice as bad. Check that last image again – it’s even obvious where the doors are.

This is one way that Google can determine where your walls are, although position data does a better job of it. But it can use these signals together to have the best picture.

Let’s take a break for a second. Did you know the Earth has a liquid molten core? How? Have you ever been there? I doubt it. Scientists haven’t been there either – so how do they know?


In reality, the interior of the Earth is where the lizard people have their hollow kingdoms, but we will ignore that particular conspiracy theory for the moment.

It’s seismology, sound, and more generally, the study of waves. (Volcanos help too.) Earthquakes, you know, are just types of waves in the Earth. Using knowledge about how different types of waves travel through different types of materials, it’s possible to figure out what materials are beneath us, all without so much as even touching a shovel.

(As an aside to this aside, this is different than how we know about the compositions of other planets, which has more to do about magnetism and solar wind, and even more different than how we know about stars, which is entirely thanks to photons and underappreciated female scientist Cecilia Payne.)

It could be possible for Google to do the exact same thing in your house. As demonstrated by science fair extraordinaire Jake H. Kuli in his 2011 USC experiment,

In testing materials such as aluminum, galvanized steel, and other conductors, the attenuation levels were high, as expected. In testing dielectrics, however, some proved to be more transparent to electromagnetic waves than expected. For example, water was one dielectric that created more dB loss than any of the metals tested. Eight feet of water attenuated the signal to the extent that it could not be detected above the surface whatsoever. On the other hand, electromagnetic waves through concrete walls showed virtually no attenuation. …

The data gathered during this experiment is easily applied in a real world setting. If line-of-sight placement of antennae is not practical, materials or objects which reflect electromagnetic waves, oriented correctly, may facilitate an adequate wireless connection between devices. Knowing the effects of signal strength on data transmission rate, an architect might specify additional wireless access points to ensure adequate network speeds. Overall, the deployment of a wireless network needs to involve scientific analysis of the environment in which it is located.

Of course, not many of us have walls made out of metal or water. But if you know a wall is there thanks to pre-existing location data, you can figure out what it could be made out of based on how easily the waves pass through. Google would certainly need to do a few studies on waves through wood, drywall, brick, etc. to get an accurate picture. But they could. Easily.

Hollow walls may look different than walls full of fiberglass insulation, which may be a lot different than other types of insulation, which is almost definitely different than brick. And don’t forget about those dead bodies! On the upside, if your great-great-grandmother stashed a billion dollars worth of gold in your walls, you can find that too. (Be wary if Google tries to buy your house after this feature launches.)

Don’t forget, in addition to your router and wifi data, there will also be times when you forget to connect, or when you have a guest over. Either way, those phones will be connected to cell towers instead. That gives Google an additional layer of data – or perhaps three layers of data, since cell towers are so good at triangulating – to use alongside the wireless info.

It’s a whole mess of data, but on the other hand, that’s kind of Google’s thing, y’know?

Wait, But Why Would Google Even Want To Know This?

Drafty in the winter? Google knows your hollow walls are letting the cold air in – especially that east one. Get ready for a whole bunch of seemingly-unprompted ads for insulation.

Just kidding. (Kind of. Not really. When it happens, you heard it here first.)

In reality, I’m not sure why Google would want this information. Google has historically wanted every scrap of information it could get, though, so it’s not too far out to think it might try and get more of this sort. Hell, maybe the head of whatever division leads this effort is a plant from the NSA.


“Anderson, great work, just one thing – is there a reason you dress like a spy when you come to work every day?” “YES – I mean – no, no reason at all. Phew, that was close.”

I won’t try to give them a motive. It’s simply beneficial to speculate about an entity’s maximum capabilities.

This Seems Sketchy. Is This Legal?

Mostly, generally, yes. You’d probably be agreeing to privacy policies that gave you anything but privacy, but how often do you read privacy policies in the first place?

(I read every privacy policy.)

More importantly, how often does the average consumer read the privacy policy for their phones? Yeah, not so often. So by using it, you’d be agreeing to it. It’s as simple as that.

Of course, they “anonymize” the data by removing all your personal information. All they’d keep was the entire layout of your home as well as your habits when you’re there. But, y’know, “anonymously”.

Sure, yeah, that seems right.

A little more importantly, though, it wouldn’t be legal for police to use this information, at least without a warrant. (Of course, since this is a recent decision, the government is sure to challenge it – read more on this here.) At least, they can’t get it themselves from your phone.

That suggests that they’d need a warrant to order it from Google’s databases too. And perhaps Google’s anonymity provisions would make it even more difficult for them – “Well, we can only say that someone was in the kitchen with the bodies in the walls – we can’t know that it was specifically your suspect. We don’t keep that data.”

The police are one thing, of course – if Five Eyes wants the data, well, they probably have a direct line into your phone already. Oh well.


Invite Google CEO Larry Page to your home. Turn up the heat so it’s a little warmer than usual, and give him some extra salty popcorn. Naturally he’ll be thirsty, and you’ll have plenty of ice water. Encourage him to drink up. Keep refilling his glass.

Eventually he’ll stand up and rub his hands together and say, “where’s your bathroom?”

Stare at him. Don’t break eye contact. Don’t back down. “You know where my bathroom is, Larry Page. Don’t try to hide it. You know.

His face will turn red, half from anger and half from embarrassment. He may spit out a half-hearted denial. But he will then walk straight for your bathroom.


“You won’t like me angry. I’m not Larry Page when I’m angry. I’m Larry RAMPAGE!!!”

Because Google knows.

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  • billslawski

    Thank you. Fun post; very thoughtful look at Google mapping indoor spaces.