Counting people with WiFi | Hacker News Reader

Counting people with WiFi

phys.org

60 pointsvinchuco17 comments

A bit similar to WiSee that controlling devices with Wifi using your hands, though not counting people http://wisee.cs.washington.edu/

I noticed this effect when I was working with Zigbee mesh networks (which usually operate on 2.4 GHz like wifi). You could clearly see the S/N ratio change between working and non-working hours as people in the office came and went. I always thought it could be used as an occupancy sensor for home or building automation (I'm surprised they aren't doing this already for hotels and other commercial buildings)

Fascinating

> 'Our approach can estimate the number of people walking in an area, based on only the received power measurements of a WiFi link,' said Mostofi, a professor of electrical and computer engineering. This approach does not require people to carry WiFi-enabled telecommunications devices for them to be counted, Mostofi emphasized.

So completely passive (as long as WiFi is on and seeking a connection).

I'm not sure what you mean by passive, but one wifi card needs to send a signal to the other. Seems more active than passive.

Correct. A passive action by the user, who often just leaves WiFi on seeking mode when on the move from convenience (walking between home, work, Starbucks, Subway, friend's house, etc).

Passive of the user not taking action, I don't mean passive of the device.

I wonder if enterprise grade AP/wifi-systems expose signal levels in such a way that is easily implementable. Would be a fun project to try at my university campus, which is crowded with AP's everywhere.

Any particular reason for using WiFi, instead of relying on better tech (such as ultrasonic, radar etc)? I'm guessing that this is a solved problem in those areas.

Well, one advantage is that WiFi can be used through walls, as the article points out.

There's also the plausible deniability if you're trying to apply this technique without being noticed by someone with detection capabilities - a WiFi hotspot blends in better than most other alternatives.

Potentially no extra hardware needed?

This has been done before, with Bluetooth - and it really pissed people off.

http://www.theguardian.com/news/blog/2008/jul/21/bluetoothbl...

http://www.cityware.org.uk/

http://www.bbc.co.uk/news/technology-23665490

Not the same thing at all. These are all intrusive and dependent on the user having a device.

This article is using wifi as a sort of radar by measuring signal attenuation/interference from meatbags.

It is pretty impresive field. Some device can detect heart beat behind 10 feet of rocks.

Sounds like radar... but with wifi.

Seeing as I always switch off my wifi when out of the house, this might not always be that accurate.

> This approach does not require people to carry WiFi-enabled telecommunications devices for them to be counted, Mostofi emphasized

Darn it. Remind me to never comment on something I don't read properly. So easy to jump to assumptions when just skimming.

Never comment on something you don't read properly!

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