how do they block cell phone signals?

Yes a device by the name of jammer is used to do so...... but i can't say how does it works

yes, there is an instrument my wife is a teacher and every student in the school can't use their phone cell during the school hour..

i dont kno

yes, there is an instrument my wife is a teacher and every student in the school can't use their phone cell during the school hour..

Frequency jammers. I have one, it sends out differant wave lengths of false signals corrupting any exicting signals in the area. Imagine you have your drop of water in a glass and you want it to get to the other side, now say i pour in a gallon of water, what happens to your drop? it gets lost in the mix, usually redirected.