Greetings. A story is making the rounds right now regarding FBI use of cell phones as remote bugs. I originally wrote about this concept in my PRIVACY Forum in 1999 ("Cell Phones Become Instant Bugs!") so the issue is real, but we still need to bring the current saga back down to earth.
This discussion doesn't only relate to "legal" bugs but also to the use of such techniques by illegal clandestine operations, and applies to physically unmodified cell phone hardware (not phones that might have had separate, specialized bugs physically installed within them by third parties).
There is no magic in cell phones. From a transmitting standpoint, they are either on or off. It is true that many phones have an alarm feature that permits them to "wake up" from a seemingly "off" state. However, this is not a universal functionality, even in advanced phones such as PDA cell phones, which now often have a "totally off" mode available as well.
It is also true that some phones can be remotely programmed by the carrier to mask or otherwise change their display and other behaviors in ways that could be used to fool the unwary user. However, this level of remote programmability is another feature that is not universal, though most modern cell phones can be easily programmed with the correct tools if you have physical access to the phones, even briefly.
But remember -- no magic! When cell phones are transmitting -- even as bugs -- certain things are going to happen every time that the alert phone user can often notice.
First, when the phone is operating as a bug, regular calls can't be taking place in almost all cases. A well designed bug program could try to minimize the obviousness of this by quickly dropping the bug call if the phone owner tried to make an outgoing call, or drop the bug connection if an incoming call tried to ring through. But if the bug is up and running, that's the only transmission path that is available on the phone at that time for the vast majority of currently deployed cell phones.
New "3G" phones have the capability of running very high speed data -- in which additional voice channels could be simultaneously transmitted at full speed along with the primary call (conventional GSM data channels -- GPRS/EDGE -- typically block calls while actively transmitting or receiving user data). But this is pretty bleeding-edge stuff for now, and not an issue for the vast majority of current phones, especially in the U.S. at this time.
Of course, if a cell phone is being used as a remote bug, the odds are that the routine conversations through that phone are also being monitored, right? So this "one call at a time" aspect isn't as much of a limitation to bugging as might otherwise be expected.
Want to make sure that your phone is really off? Taking out the battery is a really good bet. Don't worry about the stories of hidden batteries that supposedly can be activated remotely or with special codes. The concept makes no sense in general, and there just isn't room in modern cell phones for additional batteries that could supply more than a tiny bit of added power, if any (e.g., enough juice to keep phones' internal clocks going during main battery replacements, but nowhere near enough to be practical for transmitting purposes).
But if your battery seems to be running out of juice far too early (despite what the phone's battery status display might claim), that might be an indication that your phone is being used to transmit behind your back (though a worn out battery or inaccurate battery status display could also be the culprits).
Another clue that a phone may have been transmitting without your permission is if it seems unexpectedly warm. You've probably noticed how most cell phones heat up, especially on longer calls. This is normal, but if you haven't been on any calls for a while and your cell phone is warm as if long calls were in progress, you have another red flag indication of something odd perhaps going on.
Finally, if you use a GSM phone (like the vast majority of phones around the world, including Cingular and T-Mobile in the U.S.) you have a virtually foolproof way to know if you phone is secretly transmitting in voice mode. You've probably noticed the "buzzing" interference that these phones tend to make in nearby speakers when calls or data transmissions are in progress. A certain amount of periodic routine communications between cell phones and the networks will occur while the phones are powered on -- even when calls are not in progress -- so short bursts of buzzing between calls (and when turning the phones on or off) are normal.
But if you're not on a call, and you hear a continuing rapid buzz-buzz-buzz in nearby speakers that lasts more than a few seconds and gets louder as you approach with your phone, well, the odds are that your phone is busily transmitting, and bugging is a definite possibility. Note that this particular test is much less reliable with non-GSM phones that use CDMA (e.g. Sprint/Verizon phones), since CDMA's technology is less prone to producing easily audible local interference. This strongly suggests that CDMA phones may be preferred for such bugging operations. A variant form of CDMA (called "WCDMA") can be used for the high speed data channel and voice calls on the new 3G GSM backwards-compatible phones. Since additional voice channels could theoretically be encoded onto that data stream as I mentioned above -- which would be harder to detect via interference than an ordinary GSM voice channel -- this is a technology that will bear watching.
Most of this discussion applies to bugging in real time. If "delayed" bugging is acceptable, there is another approach available that would be more difficult to detect -- record ambient audio from the phone mic and store it in the phone's memory in compressed form, then upload it en masse later. Modern phones have plenty of available memory, especially ones with cameras, mp3 capabilities, and the like. The processing requirements of a delayed bug would probably be beyond the capabilities of some low-end phones, but even most entry-level phones are relatively powerful these days.
When the recorded audio was uploaded all of the transmission factors mentioned above would come into play, but since the transmission time would be shorter this would be harder to detect. Probably the biggest giveaway to this type of bugging would be battery drain, which would typically be quite considerable even in a voice-controlled recording (VOX) mode. So, my comments above about unusually poor battery performance would be especially applicable in this case.
The odds of most people being targeted for bugging are quite small. But it's always better to know the technical realities. Don't be paranoid, but be careful.