... I have yet to note any change in detector performance from a cell phone in my pocket, and I carry one with me all the time.
I mean, the amount of power emitted by a transmitting cellie is exceedingly low. An idling one emits no signal, ergo, no RF power is present to disrupt a detector.
But, leave off transmit power for a moment.
Equally as important is frequency. All tuned RF devices (those that transmit and receive) operate at a given, specific frequency.
VLF detectors operate on a frequency typically around 6-15 khz.
Cellies, on the other hand operate in two drastically different freq. ranges: 850 mhz and 1.900 ghz.
NOTE: These latter two are both microwave frequencies, that is true. That is, they are within the microwave frequency spectrum.
But they are not the same focused, highpower RF as emitted within, say, a microwave oven or by a tower mounted line-of-sight antenna.
Now, for a transmitted frequency to be coupled into a receiver of any kind, it must be either a direct frequency match or a tuned harmonic derivitive (divided) .
This is why you must "tune" your car's radio receiver to a specific frequency - to match it to the transmitted freq of the station you wish to listen to.
If this were not so, then ALL RF signals could or would be received by any receiver that happened to be on.
That being said, a cellies transmit frequency must be either a direct match to your detector's emitted signal ( which it isn't! ) or a harmonic match ( it might be ).
Otherwise, in cannot be coupled through the detectors tuned antenna/receive circuit and "wreak havoc" with the detector.
Since a direct frequency match is completely out of the question, we must look at harmonic freq's.
Here's where power comes back into the equation, and where we find the proverbial "fly in the ointment" .......
The further from the original source freq the harmonic is, even if it is sympathetic (evenly divisible), the less power it has. To make matters worse, this decay is geomotricly halved at each evenly divisible harmonic. Unsympathetic harmonics (NOT evenly divisible) have even less of the originally transmitted power.
When you consider that digital cellies transmit something like 0.3W of power at the antenna, a harmonic as close as even 1/4 wavelength away would have so little of the original transmit power as to be laughable.
So how far removed from a cellies 850 mhz is the harmonic equivalent that is your detectors operating frequency?
Using very rough estimates, about 121,000 times removed.
What would be the power in the distant cellie harmonic?
About 2.4 uW, or less - pretty small.
Now, detector receive circuits are exceedingly sensitive, I'll give you that. But, they are also shielded from outside EMF and the coil, by virtue of being a loop antenna, is highly directional. That is, it receives signals best from a certain direction only, which happens to directly below and above it. The effects of such a small amount of power as a cellphone emits on what is essentially the fringe of directional reception would be... well, questionable, even for a detectors sensitive circuits.
However, in the interests of fairness and scientific certainty, I will deliberately attempt to disrupt my detector by transmitting a cell call while in use. I'll do it tomorrow.
But to date, an idling (non transmitting) cellie in my pocket has caused no issues whatsoever with my detectors. As I said in the beginning, I carry one all the time, and it is always turned on.
For the record, no transmitting cell-phone of mine that I know of has caused a problem either, but I'll give it a try to be thourough.
In summary, the idea of a cellie disrupting a detector seems far-fetched.
It sounds more like the similar admonition to not operate a cellie while refueling your car - just another scare tactic.
