In the photo below you will see an example of wireless headphones. The transmitter which is the black box with the cable & plug is usually velcro-ed to the coil rod. The plug then is inserted in the headphone jack just like a normal set of headphones. The headphones have an RF receiver built in that demodulates the RF signal and voila detector tones arrive at your ears.
[attachment 74421 WirelessHeadpHs.jpg]
Now the picture is just an example of a product that uses a lightweight collapsing type headset. There are probably hundreds of types available when you consider some are full coverage cans, on the ear, in the ear buds etc. Then the choice of Bluetooth, AM, FM, or ISM band transmission. The growth of the portable MP3 players & i-pods etc really caused an explosion of this type of product. The Chinese factories are spitting these things out in the tens of millions a year.
Rather than look in a detector shop which may or may not carry them, just point your browser at Amazon.com and type in "wireless headphones" for a search term. If you're really really bored, you can spend hours there window(s)
shopping.
My concern with interference is not just that you have a transmitter in close proximity to the detector, but that via the headphone jack cable it is now directly coupled into the detector circuit. I don't want to get into any long electronics discussion that will just bore everyone to tears, but suffice it to say the the transmitter now has a direct path into the detector which bypasses the internal shielding of the detector. Whether or not this will cause any issues has to be experimented with on a case by case basis. In other words, how does a particular headset co-exist with a particular brand/model detector? Let's say you hook up a given transmitter to an X50 and it works fine, hook it up to a Fisher F75 and the display turns into a pinball machine on tilt.
As far as headphone use, I have several, Nugget Busters for full size cans, several Koss's, on ear, lightweight open type, some back up Rat Shack full cans, some very old back up White's branded etc. In other words, I have backups for my backups...........I have too many headphones.
HH
BarnacleBill