C. T. S Technology Co. Limited 10~16m 2400MW Hand-Held 3G Cell Phone Signal Blocker Jammer CTS-1000HB

The Cell Phone Signal Blocker Jammer CTS-1000HB, provides acoustics isolation, the ultimate solution in any area where cellular communications frequently cause nuisance either by loud incoming call rings or resulting loud telephone conversations.

A phone jammer transmits low-powered radio signals to cut off communications between cell phones and cell base stations. It does not interfere with any communications other than cellular phones within the defined regulated zone. Upon activating a phone jammer, all idle phones will indicate "NO NETWORK." Incoming calls are blocked as if the cellular hand phone were off. When the phone jammer is turned off, all cell hand phones will automatically re-establish communications and provide full service. The jamming area is influenced by the location of the cell tower and the obstacles between cell tower and the cellular jammer. It means that in normal conditions, if the distance is close between the cell tower and the phone jammer, it will have less jamming area.

I've tried it successfully in my college activities,cell phone jammers can prevent students from SMS cheating.