Using jammers can block many signals At present, the mobile phone signal jammers used in the examination room are all full frequency bands, which can interfere with all the frequency bands of the three operators 2G/3G/4G/5G, and WIFI signals and Bluetooth signals can also be shielded. The above is the principle of mobile phone signal jammer. However, the frequency band of electromagnetic waves ranges from a few Hz to several hundreds of GHz, and each segment may be used as a communication signal. Will there be some special frequency bands that are used in the examination room? This is true for other radio communication tools, and radio communication tools with dedicated frequency bands "came into being" in this context. http://www.jammer-buy.com/cell-phone-jammer/c-24.html