A high-power jammer is a signal jammer that can block any wireless signals within range. It works by transmitting a stronger signal than the original signal, thus drowning out the original signal. High power jammers are commonly used in prisons, schools, and other places where there is concern about unauthorized communications. They can block a variety of signals including cellular phones, pagers, cordless telephones, two-way radios, walkie-talkies, and even satellite signals. They are also useful for blocking wireless networks and preventing eavesdropping.