Comment on Stop Using Your Face or Thumb to Unlock Your Phone
dhork@lemmy.world 6 months agoI think you are overestimating what these devices can do when turned off, specifically when whoever is doing the tracking wants to be covert. Devices like Cellular Radios and GPS chipsets are getting more efficient every year, but they still consume enough power that it would be noticed if they came on by themselves even if the device was off.
Aceticon@lemmy.world 6 months ago
I have an EE degree and have actually done work with embedded systems, including GPS.
The peak consumption of things like GPS is maybe 100 milliamps, with the average being in the tens of milliamps.
The wireless networking stuff is similarly frugal.
Further, stuff like encoding of audio is all done on the hardware and very efficient so even voice capture and encoding to send over the network isn’t processor intensive.
Further, the CPUs on those things are ARM designs or equivalent, specifically crafted for low consumption and which have tons of tricks to avoid spending even a mW extra of power if it’s not needed (basically the CPU will tend to activate only the bits it needs and use only the resources it needs to accomplish the operations its running, so it’s almost never running at peak consumption).
The really big power consumption in modern smartphones is the screen and from very high GPU/CPU usage in things like games.
I think you seriously overestimate the similarity between modern portable devices design to operate from quite small batteries and things like desktop Personal Computers which are designed to operate from mains.
If all they’re doing is sending your GPS position out over the netweork every couple of minutes you won’t notice that the battery has drained a tiny bit faster than expected.
dhork@lemmy.world 6 months ago
Doesn’t a modern smartphone have something like a 4000 mAH battery? And that lasts most people all day with room to spare? Even 100 mA every few minutes will get noticed, if someone has their phone off and expecting consumption to stay minimal.
And that’s the key thing here, you’re not just building a tracking platform but you are building it into commodity phone hardware without the users consent, and without them noticing. Any phone that burns that much power while off would likely get replaced by the user. Do you think the phone vendors are in on it?
Aceticon@lemmy.world 6 months ago
It’s not 100mA every few minutes, it’s 100mA when calibrating from scratch with no satellites known.
I looked it up and the consumption when in normal use is around 30mA, which would mean that, say, if it took 10 seconds (probably a lot more than needed if you’re not travelling) every 5 minutes - which adds up to 120 seconds @ 30mA per hour - would consume 1mA/h (by pure absolute chance my numbers ended yielding a result of 1 ;)), which is 0.025% of that battery per hour. If you’re lucky, in the phone screen were one would be visualizing the graph for the battery power charge over time that would show the line falling by 1 pixel.
It really is a whole other world out there in the embedded and low power systems domain.
dhork@lemmy.world 6 months ago
In order to not “start from scratch”, though, you will need to save some state persistently about your location (and the location of the satellites), which will cost power. Then you go in a building and lose all your signal, while still burning power to maintain that old state.
If it was that easy and cheap in terms of power, AirTags would have GPS receivers. They don’t.