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Displays Power Hardware

Sonar Software Detects Laptop User Presence 167

Steve Tarzia writes "A research group at Northwestern University and University of Michigan has released open-source display power-management software that uses a new user presence detection technique. The goal is to shut off the display immediately when the user leaves the computer rather than using slow and error-prone mouse/keyboard activity timeouts. Surprisingly, the mic and speakers of many laptop computers are sensitive to ultrasonic frequencies. Those frequencies can be used to silently probe the laptop's physical environment. This software is based on research published at the UbiComp2009 conference. A Windows binary and source code for Windows and Linux are available for download."
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Sonar Software Detects Laptop User Presence

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  • by Anonymous Coward on Thursday October 15, 2009 @05:41PM (#29762995)

    Don't time your screensaver so aggressively. Turning the screen off after just a few minutes is useless and just puts unnecessary strain on the backlight (which takes only a limited number of power cycles, unless it is LED).

    I use Ampsoft's Screen Saver Control [] to manually put the screen into power saving mode with Win+P (and the standard Win+L to lock the screen, if I think that's necessary). I have set the power saving mode to kick in after 2 hours of inactivity otherwise.

  • Re:Activity (Score:3, Informative)

    by Chris Burke ( 6130 ) on Thursday October 15, 2009 @05:45PM (#29763045) Homepage

    Mouse/keyboard activity timeout works nicely for that.

    Er not really. You need to set it to long enough that it doesn't time out every time you read a page of text (unless you just like idly dragging the mouse around while reading... i don't). Yet you want it short enough that it provides power savings. The LCD screen is a big power hog in a laptop. Being able to turn it off instantly as soon as you walk away, and turn back on when you sit back down, would be the best of both worlds of power savings and convenience.

    I rather don't have the computer know if I'm walking near it or not. But it seems we're heading in to this "everyone, and every machine, knows where you are" every day.

    Yeah I'd be more worried about the fact that your computer knows every single thing you type, and every single thing you read. ZOMG!

    But seriously. It knows whether you are in front of your laptop or not. Are you often running your laptop when you aren't around at all, such that the assumption that your laptop being on and connected to the network is generally accurate? Like it's a big danger that the laptop knows you aren't there anymore when you get up for a quick piss break. Not that it knows you went to the bathroom!

    Besides, it's open source. If you're that worried that it's going to report your location to The Man, check the source code.

    And hey, if you're really worried about realistic ways for The Man to find you, take the battery out of your cellphone. Seriously, that's a real way in which the phone company/police can locate you.

  • Re:Activity (Score:2, Informative)

    by jijacob ( 943393 ) on Thursday October 15, 2009 @06:17PM (#29763417) Homepage
    I use blueproximity on ubuntu. Set the distance and it works pretty well to lock (and unlock) my computer when I am away. The unlock could, I'm sure, be easily spoofed, so if you were in a high-sensitivity location you might want to disable the second half of this software.
  • Re:Activity (Score:4, Informative)

    by Bottlemaster ( 449635 ) on Thursday October 15, 2009 @08:04PM (#29764417)

    granting an application access to the microphone should really be some security feature in the OS. By far none of the Windows, Linux, Mac or BSD are doing it

    You're right about Windows, and I don't know about Mac. But BSD and Linux have had this for as long as they've had audio recording. For example, on my FreeBSD desktop:

    $ ls -l /dev/dsp*
    crw-rw---- 1 root wheel 0, 106 Oct 14 23:57 /dev/dsp0.0

    A program must be running as root or group wheel to record audio. In this case, I could whitelist apps by setting the group owner to wheel and setting the SGID bit. I'd probably create a seperate audio group if I cared about recording permissions and had a mic connected. You can get even more granularity with ACLs.

  • Dimmer switches buzz at 50/60Hz (with lots of metallic-sounding harmonics). Everyone hears those. Better designed ones make less noise. Battery chargers and power adapters in general (of any kind) either buzz at 50/60Hz (transformer based) or at a higher frequency (switching type). Poorly designed switching converters might operate in the audible range - I have a few that can definitely be heard. Most good ones are well above 20Khz. CRT TVs operate at ~15Khz; I hear those too. CRT monitors operate well above 20Khz; ~30Khz for 640x480 VGA (horizontal frequency). I doubt you can hear those. Maybe some specific monitor that produces noise at a division of the frequency?

    I tried this on my laptop and I couldn't hear anything (other than some clicks when it is enabled/disabled, due to poor switching). The debug log says it's generating 22Khz pulses. It didn't work too well on my machine though.

Each new user of a new system uncovers a new class of bugs. -- Kernighan