Dispositif Anti-Pillage: The French have one, why have not the Brits or Americans?

Although I can see at the moment very few in the "likes" or "friends" of this facebook page, one assumes every UK detectorist will speedily welcome this, especially NCMD who are members of the Alliance to Reduce Crimes Against Heritage, and the staff of the British Museum's Portable Antiquities Scheme: http://www.facebook.com/dispositif.antipillage.1

According to its manufacturers, the device can be set up to protect an area of a few square metres up to a few thousand square metres, is powered by 4 LR14 batteries which will keep it operating for a year unattended. The device remains in standby state with little energy consumption until it detects the approach of a metal detector, when it begins to transmit an interference signal. The jamming signals create electromagnetic interference, preventing the use of metal detectors within the protected area - so far no health risks to would-be looters from the electromagnetic field have been ascertained (metal detectors create such a field potentially creating harmful nanovibrations anyway). The source of the interference is difficult for the looter to detect, as the field strength of the signal is the same throughout the protected area. In any case, it seems to me adding an alarm (and perhaps cameras) which would be activated by any attempt to interfere with the device would allow the collection of evidence leading to prosecution in addition to the device protecting a site of importance.

So how many is English Heritage buying for its pilot scheme?