Cell phones aren't just receivers. They are transceivers, meaning they have a radio for receiving a signal from the cell tower, and a transmitter for sending signals back. Not only should it be easy to detect a cell phone, the technology already exists.

My understanding is that in Iraq, locals know to expect a cell phone outage if they see an American patrol coming, since jamming equipment is already in common use as a means of defeating IEDs.

To stay ready to receive a call, a cellphone has to periodically send a short signal to tell the cell system where it is. Otherwise, the system won't know which tower to send the incoming call to. That signal is full strength and detectable at the same range as a cell call is, but I don't see a way to tell whether the cellphone is in an IED or clipped to someone's belt.

Also, any receiver will emit some RF from it's local oscillator. At short range, this makes it continuously detectable. This is wasted power, so the engineers will work especially hard to minimize this signal in a device that has to work from a small battery - that is, in cellphones. So the detectability range might be closer than you'd want to be when you detect an IED, but OK for a robot sent ahead of the convoy. The problem, once again, is how does the robot determine if the cellphone running inside a parked car is hooked to an IED detonator, or is just in the pocket of someone parked on the side of the road.

So jamming all cellphones while you pass seems like a good idea. It's not a perfect idea. It would be possible to rig a jamming detector and use that to set off the bomb, but this is much, much harder than just wiring the ringer to a blasting cap.

Have you seen these? They started building these for high profile security details, bomb squads among others. The military has similar items. Detecting is easy, figuring out what to do with what you find is the tough part. The problem is if you have a reverse signal (where a lost signal is the trigger). Only and EMP would really stop all of the options on triggering an IED.

Much simpler to use high powered wide-band jammers. Takes out all sources of radio triggeringing, not just cell phones(like garage door openers). Only ways left are wired and IR. Harder to defeat but range is a problem for the attacker.

My son just got back. He says that the vast majority of the command detonated radio IEDs are triggered from a simple Motorola FRS set. The bad guys use a wind-up timer, like on a toaster, to keep stray signals from triggering it while they are arming it, but once the timer finishes, a simple call into the tone-keyed receiver and... boom. Total cost; 2 bucks for the timer and 18 bucks for the pair of FRS radios.

Cell phone triggers are passe'.

email is human readable - aloud.

The IDF is reported to have solved this problem with an oscillating transmitter that sends powerful signals in random codes. The equipment is large, and takes a 5-ton vehicle or Super Blackhawk to carry.

The system can be tuned for either the generic R/C detonators that the paleo-terrorists invented (or got from the CCCP years ago), or cell phones, or even plain command-detonated explosives belts. There haven't been many successful strikes against IDF outposts in the last couple of years, but there HAVE been quite a few "bomb blew up prematurely" cases where bombers were deconstructed in the process.

Rumor also has it that the US refused to use the equipment due to it's huge directed energy issues. In other words, it can fry people as well as 'splode splodey-dopes.

What gets me is the fact that a simple modification to the cell sites, necessitating the use of newer cell phones that are tamper-proof could eliminate most of these phone-detonators. Why haven't we insisted on that?