My friend (I don't know him in person, we work together remotely) told me that he has 3 cell phones: one at home, one at the work-place and one always turned-off in his car (for emergency). He doesn't wear a cell phone with him. When someone wants to contact him he/she calls him on one of his home/work phones judging from the day time, if he doesn't answer the call he calls back when he reaches home/work place and sees unanswered calls.

Two years ago when he told me this I thought he is a tinfoil-hat paranoid person but now I know he is right.

He's not being paranoid enough. A guy with a cellphone that never leaves the home? Any decent data analysis software should flag such an odd behavior. If one's not willing to fully disappear off the map, the safest behavior is to provide "boring" data in order to blend in with the crowd.

Or you could just, you know, not carry a radio-transmitter on you while committing some possibly illegal/disruptive activity?

One could not want to have some legal but disruptive to certain interests or usable as future blackmail material captured, stored and analyzed.

Just turn it off?

That's ok if you have the money.

But if you hang out just a little bit with pot heads in eastern Europe you know the best solution is to turn off your phone and take the battery out when you don't want people tracing you or lightening to your conversations.

There is only 1 real solution:

Put your cell phone in flight mode and use it exclusively as a PDA/music player/etc.

Let people contact you on a landline and email - more than enough.

I'm pretty sure this doesn't work. i.e. even in flight mode, the baseband processor is still powered and will passively listen for cell-tower requests, so presumably it can still be told to wake up?

I know its true of phones that are "off" without the battery removed - stands to reason it applies in flight mode too.

Technically this isn't true, at least not as a blanket statement regarding all phones.

Since the power button is a 'soft' switch, controlled by the phones operating system, it's possible that a phone can be compromised so that even if it appears to be 'off' it is actually still powered up and listening to the cell network, but this is in no way a 'standard' feature. The same attack vector/vulnerability is present for flight mode, a compromised phone can lie and report that the radio is off when malicious software is using it.

Removing the battery is a mechanism to preclude any possibility of your phone being exploited, and may be appropriate depending on your risk tolerance and/or threat model.

Can also go into recovery and nuke the baseband stack modem.img since wifi only needs the application OS kernel.

I've not seen any evidence this is the case without explicit tampering with the phone (i.e. installing spyware which then fakes the 'off' state in software).

It's in the patriot act that the government is allowed to do it, so I'd imagine it is possible.

afaik, actually wrapping the phone in tinfoil blocks the signals pretty well. try it, you can't call a phone wrapped in tinfoil.

if you have a tinfoil lined bag (like a thermo lunchbag), it's even easier than removing the battery.

Flight mode does not make you untraceable - it just makes your phone less useful.

If you're doing something illegal, or talking to someone about something illegal, leave your phone at home, and use your $15 dumbphone with an unregistered throwaway sim.

Or rather, buy a PDA/music player rather than a phone.

@JetSpiegel http://www.apple.com/ipod-touch/

Where can I buy one of those? Haven't seen an MP3 player or a PDA for sale in ages.

That's a good idea. You won't be able to stream something live anymore, though, but I guess either you record it and later upload it to websites, or some people will have to take the chance to stream it.

Get a burner phone, even from a different country. I have a Russian and French sim cards and keep your phone off unless you really need to make a call.

Check that the phone's IMEI isn't also being associated with each of those SIM cards and your regular one.

Just switching SIM cards may change what account info you're using, while still providing plenty of information for determined investigators to use.

It can be technical in nature, but the society needs to request it from the carriers and also the government to allow them to have such high security in place, and not allow them to wiretap and have access to everything. When the government says "but we need access to everything to catch a criminal". The society must respond "Oh yeah? Well screw you - I think my privacy is more important, and I want better end-to-end security for my conversations and metadata".

The solution can be political, too, and it would certainly help, but I think it's a lot less sustainable from government to government.

But "society must respond" is a political solution, not technical.