Cellphone jammers are illegal in most countries (the military excepted) but in France, since 2004, it is legal to use jammers in cinemas and theatres.
A cellphone jammer is a device that emits signals in the same frequency range that cellphones use, effectively blocking their transmissions by creating strong interference. In Europe those frequencies are gsm 900MHZ and gsm 1900 MHz.
Someone using a cellphone in the range of a jammer will lose signal, but have no way of knowing a jammer was the reason. The phone will simply indicate poor reception strength. A “jammed” environment in a cinema is basically the equivalent of putting people in a more concentrated electromagnetic radiation incubator, so it’s worth asking how safe this is, especially for young children.
Jammers can be useful for security; say a presidential motorcade, to keep terrorists from detonating a bomb by cellphone. The potential health risk associated with these “jammed” environments has been raised by the case of Belgian soldiers operating in Afghanistan who started showing symptoms of electrohypersensitivity last August – nausea, headaches etc. The suspected cause is the jammer installed in their armoured vehicles – Lockheed Martin’s Symphony IED jammer system – which protects them from cellphone detonated explosions.
While the Belgian Defense Ministry insists that the level of radiation was within acceptable norms, an investigation has been opened and two of the soldiers in the 11th Engineer Battalion in Burcht have been removed from service by doctors.
Meanwhile, in France, the “Grenelle des Ondes” wrapped up a month-long consultation which was so weak-kneed that the NGO’s quit the proceedings before the end, declaring the exercise a farce. No conclusions were reached on the thorny question of cellphone basetowers; proposals were put forward to ban cellphones from elementary school grounds, for telephone operators to offer child-friendly cellphone plans that only allow text-messaging and start selling phones that can only be used with an earpiece.