# When a mobile phone is off, what does it continue to do? **URL:** \ **Category:** Factual Questions\ **Created:** [April 24, 2014, 6:28pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880 "2014-04-24T18:28:24Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [April 30, 2014, 2:11pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/21 "2014-04-30T14:11:04Z")
> [@Francis\_Vaughan](#): > > That said, any device with a soft power button requires some basic operation of the device to continue. Phones contain a number of processors, and the power management chip alone can be smart enough to watch the power button, as well as manage the rest of the phone. The main processing systems will be powered down, as will the RF systems (of which a smartphone has many.) I think my dumb phone’s alarm still works when it’s shutdown. In addition to turning on only when the power button is held (not just pressed briefly - indicating some intelligence), I think the phone is using power and processing on at least a low level. As to whether this low level allows communication, or can be hacked to do so, I’m guessing it depends on the phone model? ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [April 30, 2014, 4:01pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/22 "2014-04-30T16:01:34Z")
> [@AaronX](#): > > I think my dumb phone’s alarm still works when it’s shutdown. I’ve read descriptions of alarms and how phones can wake up briefly just enough to see if a timer has triggered, then go off again. It’s very low level and barely wakes up the phone enough to do anything. Little processing is occurring, just a quick check for a known trigger to wake up. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [April 30, 2014, 5:32pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/23 "2014-04-30T17:32:45Z")
> [@Little\_Pig](#): > > If you’re still concerned at this point[then buy one of these.](http://www.amazon.com/gp/product/B00GSZI24M/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1) End of thread. You’re assuming the thread is about concern, but it’s about curiosity. So, not end of thread. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [April 30, 2014, 5:40pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/24 "2014-04-30T17:40:11Z")
> [@Telemark](#): > > I’ve read descriptions of alarms and how phones can wake up briefly just enough to see if a timer has triggered, then go off again. It’s very low level and barely wakes up the phone enough to do anything. Little processing is occurring, just a quick check for a known trigger to wake up. Right, and it’s the ability to do stuff like this (and other things) that could give spyware the ability to communicate when the phone appears to be off. Of course, it would consume more battery power while “off” than normal, but possibly not very much. I’m confident that spyware could do this. The newsy show I mentioned in the OP made it sound like an uncracked phone could be tracked when powered off. My guess is that it can’t be. So, if my phone hasn’t updated the OS recently, and all of a sudden I have reason to be fear being tracked by someone, I think I’d be safe just turning it off. Or putting it in a faraday cage, as **Little\_pig** suggests. Meanwhile, I’ll buy up some bitcoins so I’ll be able to get some money while I’m off the grid … 🙂 ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [April 30, 2014, 5:56pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/25 "2014-04-30T17:56:18Z")
> [@Learjeff](#): > > Right, and it’s the ability to do stuff like this (and other things) that could give spyware the ability to communicate when the phone appears to be off. Of course, it would consume more battery power while “off” than normal, but possibly not very much. > > I’m confident that spyware could do this. The newsy show I mentioned in the OP made it sound like an uncracked phone could be tracked when powered off. My guess is that it can’t be. > > So, if my phone hasn’t updated the OS recently, and all of a sudden I have reason to be fear being tracked by someone, I think I’d be safe just turning it off. > > Or putting it in a faraday cage, as **Little\_pig** suggests. Meanwhile, I’ll buy up some bitcoins so I’ll be able to get some money while I’m off the grid … 🙂 I don’t think that’s possible on a smartphone (like an iPhone). Look at how long the phone takes to boot from the off state! Dumbphones that had a very-low-power sleep mode could do this, because the RTC could wake the phone quickly enough in response to an alarm. Smartphones don’t have the same type of alarms - they only run when the OS is running (which, BTW, is almost always a Unix or Linux variant). ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [April 30, 2014, 6:50pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/26 "2014-04-30T18:50:39Z")
> [@beowulff](#): > > I don’t think that’s possible on a smartphone (like an iPhone). > Look at how long the phone takes to boot from the off state! No kidding. As an embedded systems programmer, I’m familiar with how tricky it can be to try to use just some subsytems from an OS, without bringing up the full OS. But I don’t have any Android or OSX experience or phone communications systems, and I’m frequently amazed at what people can do, including both hackers and the open source community. It’s also amusing how the embedded systems model has changed. I used to write code that practically “ran on bare metal”, then used very thin real-time OSs. Today, code I write to run in internet routers runs on Linux. Linux even runs on most of the the “line cards”, not just the supervisor “brain” card. It’s a blessing and a curse. 🙂 ---
**Author:** ![Little\_Pig](https://avatars.discourse-cdn.com/v4/letter/l/c57346/32.png) [@Little\_Pig](https://boards.straightdope.com/u/Little_Pig)\ **Post date:** [April 30, 2014, 7:38pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/27 "2014-04-30T19:38:29Z")
> [@Learjeff](#): > > You’re assuming the thread is about concern, but it’s about curiosity. So, not end of thread. Agreed. Question. How does a Faraday Cage work? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [April 30, 2014, 7:56pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/28 "2014-04-30T19:56:32Z")
> [@Little\_Pig](#): > > Agreed. Question. How does a Faraday Cage work? Just solve Maxwell’s equations… Basically, radio waves can’t pass through a conductive enclosure. As long as the inside is completely isolated from the outside, any conductive material will do. The bags use a metalized plastic, and have some type of seal that makes decent contact with the two edges. Since both the material and the seal aren’t that great, the reduction in RF energy is on 65db (which is still over 1 million times). ---
**Author:** ![usedtobe](https://avatars.discourse-cdn.com/v4/letter/u/ec9cab/32.png) [@usedtobe](https://boards.straightdope.com/u/usedtobe)\ **Post date:** [April 30, 2014, 11:19pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/29 "2014-04-30T23:19:29Z")
Faraday cage for a phone? If I go to the (real) hardware store and buy a bit of copper window screen and form it into a liner for my phone’s case (except that there is no way to “open” the liner - use a stylus to push buttons), do I defeat some/all of the nefarious uses to which any number of people are going to find for a device simply everybody carriers - willingly! (I am the last person many people know as “the guy WITHOUT a cell - can you imagine!”) If the gov’t had said "Here’s a box which will automatically tell any/everyone interested: Its unique ID Location Motion, including speed and acceleration, in 3 dimensions Every number you call, where, when, for how long (what am I missing?). Please carry it with you 7/24. How many would do so? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [April 30, 2014, 11:37pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/30 "2014-04-30T23:37:42Z")
> [@usedtobe](#): > > Faraday cage for a phone? > > If I go to the (real) hardware store and buy a bit of copper window screen and form it into a liner for my phone’s case (except that there is no way to “open” the liner - use a stylus to push buttons), do I defeat some/all of the nefarious uses to which any number of people are going to find for a device simply everybody carriers - willingly! > > (I am the last person many people know as “the guy WITHOUT a cell - can you imagine!”) > > If the gov’t had said "Here’s a box which will automatically tell any/everyone interested: > Its unique ID > Location > Motion, including speed and acceleration, in 3 dimensions > Every number you call, where, when, for how long > (what am I missing?). > > Please carry it with you 7/24. > > How many would do so? Paranoid much? If you put a phone in a working Faraday cage, it’s no longer a phone. So, if you are unwilling to expose yourself to all the real (or, more likely imagined) dangers of using a cell phone, don’t own one! ---
**Author:** ![Bert\_Nobbins](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@Bert\_Nobbins](https://boards.straightdope.com/u/Bert_Nobbins)\ **Post date:** [May 1, 2014, 12:57am UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/31 "2014-05-01T00:57:05Z")
One-time dumb-phone designer here. As already noted, “off” is not really off as if it was you could not use the phone as an alarm clock. It is perfectly possible to have the microphone active and transmit audio while the phone is “off”, if the right software is loaded. If it only worked intermittently you would probably not notice the extra battery drain. Taking out the battery is a complete solution- unless of course someone has been at the hardware and added a secret extra battery. That sounds hard to do- there’s not a lot of wasted space inside phones- but 15 grams of explosive has been fitted in: [http://en.wikipedia.org/wiki/Yahya\_Ayyash](http://en.wikipedia.org/wiki/Yahya_Ayyash) ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [May 1, 2014, 2:01am UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/32 "2014-05-01T02:01:43Z")
I’ve seen phones keep their time even with the battery removed for ~1 minute. I’ve even had a camera that could keep time while the battery was charging outside - 2 hours! Although, I think sensors and radios won’t work in this state. It just shows that: Device destroyed Battery removed Shutdown Are distinct, at least in some devices. ---
**Author:** ![Little\_Pig](https://avatars.discourse-cdn.com/v4/letter/l/c57346/32.png) [@Little\_Pig](https://boards.straightdope.com/u/Little_Pig)\ **Post date:** [May 1, 2014, 3:00am UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/33 "2014-05-01T03:00:24Z")
> [@beowulff](#): > > Just solve Maxwell’s equations… Jeepers Creepers. Given the value I put on my time, I think it would be a whole lot cheaper to just buy the cage on faith. 🙂 What I be correct to assume that microwave ovens are wrapped in a Faraday cage? In keeping with this question, was it here on the SDMB where I read, to find out if your microwave leaks, put your cell phone inside, close the door, (DO NOT TURN ON MICROWAVE!), then call your cell phone? (If the phone rings, you got a leak.) ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [May 1, 2014, 3:13am UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/34 "2014-05-01T03:13:48Z")
> [@Little\_Pig](#): > > Jeepers Creepers. Given the value I put on my time, I think it would be a whole lot cheaper to just buy the cage on faith. 🙂 > > What I be correct to assume that microwave ovens are wrapped in a Faraday cage? In keeping with this question, was it here on the SDMB where I read, to find out if your microwave leaks, put your cell phone inside, close the door, (DO NOT TURN ON MICROWAVE!), then call your cell phone? (If the phone rings, you got a leak.) Yep. That’s why the door seals are so important - they need to make contact around the entire periphery, or the cage isn’t “tight.” ---
**Author:** ![Little\_Pig](https://avatars.discourse-cdn.com/v4/letter/l/c57346/32.png) [@Little\_Pig](https://boards.straightdope.com/u/Little_Pig)\ **Post date:** [May 1, 2014, 3:37am UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/35 "2014-05-01T03:37:06Z")
> [@beowulff](#): > > Yep. That’s why the door seals are so important - they need to make contact around the entire periphery, or the cage isn’t “tight.” It appears I have a “leaky” microwave… ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [May 1, 2014, 5:42am UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/36 "2014-05-01T05:42:07Z")
> [@Little\_Pig](#): > > It appears I have a “leaky” microwave… Saves money on a vasectomy, anyway… Also, if you pull the SIM card, the phone won’t communicate on the cellular network so it won’t be able to report anything. (if you pass open Wi-Fi, depending on settings, it may connect and send a “hello” to the NSA.) Of course, the NSA might have a cell tower utility that reports “the following phone asked for connection but didn’t have a SIM card…” I’m not sure what the protocol is for connecting to carriers, if it’s active or passive, whether the phone will even try or just listen to carriers that match its card. My experience with iPhone 3GS is it says “no SIM card” and does not even try to find a carrier; since the process appears to be “find carrier, pass on SIM info, see if carrier is the SIM originator or a partner and validates”. Some older removable battery phones likely had a smaller internal battery to keep things alive while changing batteries. ---
**Author:** ![Little\_Pig](https://avatars.discourse-cdn.com/v4/letter/l/c57346/32.png) [@Little\_Pig](https://boards.straightdope.com/u/Little_Pig)\ **Post date:** [May 1, 2014, 6:25am UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/37 "2014-05-01T06:25:44Z")
Amazon has emailed me with a message that my [Faraday Cage](http://www.amazon.com/gp/product/B00GSZI24M/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1) has shipped. Question. In the interest of science, if I put a hot dog in this thing and try and nuke it, would the cage get a “thumbs up” if the wiener comes out cold? ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [May 1, 2014, 8:37am UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/38 "2014-05-01T08:37:05Z")
One thing about phones is that they don’t run just one OS. At a minimum, phones are divided into two separate parts - the Application Processor - which runs the OS you see - ie iOS, Android, Windows - and the Baseband Processor - which is responsible for the cellular radio communications protocols. The BP typically runs a closed source propitiatory real time OS. This is true even of Android phones. In addition, the other radio communications chips (WiFi, Bluetooth) can run internal firmware that is independent of either the AP or BP OS. Communication between all of these elements is usually done over a simple serial bus - such as USB. It is quite possible that your phone is running 4 or 5 totally different separate and independent software systems, on a wide range of architectures. These other software systems can provide a source of security exploits, and many people are rather unprepared for the idea that the malware infecting their system is resident inside (say) the WiFi chip, and the main OS is not itself infected - or is trivially re-infected by the exploited WiFi chip. However, these are black belt exploits, and highly dependant upon the exact hardware. None the less, from at least a theoretical point of view, some remarkable exploits are possible. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [May 1, 2014, 12:33pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/39 "2014-05-01T12:33:00Z")
> [@Little\_Pig](#): > > Amazon has emailed me with a message that my [Faraday Cage](http://www.amazon.com/gp/product/B00GSZI24M/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1) has shipped. Question. In the interest of science, if I put a hot dog in this thing and try and nuke it, would the cage get a “thumbs up” if the wiener comes out cold? A Faraday cage is simply a conductive container that’s sealed to much less than the wavelengths you are trying to block. Putting a conductor in a microwave (tin foil, silverware, metal container) highly NOT recommended. The intense radio waves induce some serious currents in the metal. I’ve seen arcing and flashes from paper/foil fast food pouches. Fancy plates or cups with gold foil in the decorations may be damaged in this way. The metal also reflects the microwaves around and reinforces the strength, possibly damaging the microwave itself. Those brownish paper towels made of recycled material should not be used in a microwave because they may contain small flecks of aluminum foil from the recycling process - there is a warning the paper could burst into flames if the microwave heats the metal flecks too much. So if you have a microwave you don’t mind losing, by all means put your conductive item in it and stand back. ---
**Author:** ![Little\_Pig](https://avatars.discourse-cdn.com/v4/letter/l/c57346/32.png) [@Little\_Pig](https://boards.straightdope.com/u/Little_Pig)\ **Post date:** [May 1, 2014, 9:09pm UTC](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880/40 "2014-05-01T21:09:42Z")
> [@md2000](#): > > So if you have a microwave you don’t mind losing, by all means put your conductive item in it and stand back. Yeup, figured as such. Will test cage differently. The hot dog is still gonna nuked though. [Previous page](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880.md?page=1) [Next page](https://boards.straightdope.com/t/when-a-mobile-phone-is-off-what-does-it-continue-to-do/686880.md?page=3)