The units advertised are transmitter, not induction devices, working in the FM wide band frequecies allocated to commercial radio broadcasts (66-108mhz) and as mentioned before illegal, and liable to procecution - such low power devices rarely cause enough problems to cause interference and investigations resulting in a prosecution - unlike radio microphones which are normally higher power and also tend to drift off frequecy and cause harmonic interference as well.

Clansfolk was right in his comment, which I took as an aside, as he said he hadn't had any luck with such units implying he had used such illegal devices himself.

Doubt if feature would be switched off in UK models as most would just be "grey" imports as appose to made for the British Market and not worth the hassle - if switched off through software programing it is often easy to switch back on through keypad entries - like you can with Ham equipment and mobile phones DVD's etc.