What I do not understand, if this is a weapon, how can a country which deploys the most sensitive sensors in their embassies to listen in on their host country

What I do not understand, if this is a weapon, how can a country which deploys the most sensitive sensors in their embassies to listen in on their host country (sound, electromagnetic, gravitonic, ...), not detect this? And if it is radiation/waves that there are no sensors for, why aren't new sensors installed? So the CIA scrambles around and installs a myriad of new sensors in every embessay, and nothing after years? The opponent has not only some new kind of weapon, but a new kind of energy or rays that are not gravitational, electromagnetic or sonic? So they have a Nobel prize winning physics discovery and use it to make people in embassies sick?