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I know this is tin-foil hat fodder, but at least one judicial opinion (http://www.politechbot.com/docs/fbi.ardito.roving.bug.opinion.120106.txt) referenced a bug that could track/listen in on the subject "whether the phone was powered on or off," although that may have been a judge misinterpreting the technobabble spouted at him, or an FBI agent overhyping their tech to the judge.

It seems like with smartphones all the rage now, it would be possible, e.g. to create a root kit that would simply mimic the phone entering a powered down state while still transmitting, although this would have an obvious effect on battery life unless it actually powered down most of the time and just woke up to transmit basic location information in a heartbeat configuration. Is there anything similar out there in use by either "good guys" or "bad guys" that you know of?

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My old candy-bar dumb phone, when turned off, will still turn itself back on to sound a set alarm. So I've never assumed powering down a phone means anything except that it is in a state of deep battery conservation. – logicalscope Mar 15 '12 at 4:17
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+1 to @logicalscope. My current flip-phone does this also. The question then becomes, is the radio still active when the phone is "turned off"? – Iszi Mar 15 '12 at 4:37
Yep, they just keep on trying, poor things... Well, I remembered something about the NO SUCH AGENCY buzzing every mobile number every day to prevent terrorists from you know...being terrorists. ;-9 – user8454 Mar 15 '12 at 5:56
@Sam Skuce +1 we need more questions like this. – Rook Mar 15 '12 at 6:12
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@Iszi not proof, but whenever I go into a "highly secure" area (e.g. government, military, etc) I either have to leave my cellphone outside, or remove the battery. Some of this is "tinfoil-hat", as the OP said, but perhaps there is something to it. – AviD♦ Mar 15 '12 at 6:40
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up vote 12 down vote accepted

Who's to say that the phone is really off? If someone controls the firmware of the device then the off functionality could be replaced with state in which the phone appears to be "off" but is in fact maintaining a line of communication to a remote user.

However firmware cannot stop you from introducing a hardware switch to disconnect the microphone. A similar switch could be used to disconnect the battery. With physical control over the device you can just move to a lower layer than your attacker and cut them off.

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+1 for mentioning physical security. – Tyler K. Mar 15 '12 at 8:00
Accepted because you answered the question in the title, and it appears that no-one is willing to admit they know about such functionality being used in the real world =) – Sam Skuce Mar 20 '12 at 16:30
@Sam Skuce Yeah sorry i am not aware of this software existing int he wild. Also its not really proper to call this a rootkit per say, this functionality is below the kernel its in the firmware. – Rook Mar 20 '12 at 16:41
@Rook, yeah if it's in the firmware from the manufacturer, it's not a root-kit, it's a feature! But the (hypothetical, I want you to think) rootkit I referred to in my question is an aftermarket add-on that can be surreptitiously installed by any of the usual malware methods, so the term would be accurate. – Sam Skuce Mar 20 '12 at 16:52
@Sam Skuce an attacker can flash the device's firmware, and telco's roll out firmware updates over the network all the time to make sure devices are "working properly". – Rook Mar 20 '12 at 17:04
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As an example, iPhones do not have an accessible battery or SIM card to remove (at least on Verizon) and alerts will wake up the phone even if it is turned "off" via the UI. The software is black-box and proprietary. With one of these common phones you have no assurances of anything.

Off has a different meaning now than it used to with respect to technology. There are different levels of power consumption: hibernate, sleep, deep sleep, off, etc. Ultimately, if there is power supplied (charged battery present) you don't really know what the phone is capable of unless you examine the source code of the software running on the phone and have an assessment of its hardware capabilities.

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