Why would someone use signal jammer in residential area?
Criminals like to use these devices because cell phone jammer devices prevent victims from calling 911. For example, a thief who is not using these devices may be making a 911 call when he is at the crime scene, not far away.
Since the new method of using a cell phone on an alarm system is rather unreliable, all you need is jammer gps, and the siren can't call to report a break-in.
Of course, such a device is illegal. But if you're robbing a house and want to beat the alarm system, having a cell phone jammer makes all the difference.
There's no reason to buy specialized equipment for this, as many things can interfere with Wi-Fi signals, especially on the 2.4GHz band. Cordless phones, older non-Wi-Fi wireless devices, microwave ovens, etc. All of these can and will cause a lot of problems for anyone trying to use Wi-Fi in the area.
For example, a company called Perfect camera used to sell a wireless camera that used the 2.4GHz frequency band to send a signal from the camera to the receiver. It can wreak havoc on Wi-Fi if you try to use certain channels.
The FCC only regulates power levels for 2.4GHz devices. In order to use this frequency, all devices must tolerate any interference. So not much can be done. Tracking down the source of Wi-Fi interference is not easy and can require quite expensive equipment to locate the source. Apps you might find for your phone won't work well because they don't use directional antennas. Also, the phone won't do anything to non-Wi-Fi signals, such as interference from microwave ovens.