Terminology can sometimes confuse all of us. [Seytonic] does a good job of explaining the difference between a WiFi jammer and a cancellation validator in the video embedded below. Many of you already know the difference, but it's worth pointing it out because many refer to de-authenticating devices as "wifi blocker."
In their YouTube video, they explain that jammers emit a noise load on all WiFi channels, resulting in unusable frequencies within a given distance from the jammer. Jammers are also usually quite expensive and mostly illegal, making them hard to find unless you make your own.
WiFi de-validation, on the other hand, works in a very different way. WiFi sends unencrypted packets, called management frames. Because these are not encrypted, even if the network uses WPA2, a malicious party can send a de-authentication command to direct the user out of the access point. However, there is hope for 802.11w with encrypted management frames. It's been around for a while, but manufacturers don't seem willing to implement it, even though it could make WiFi devices more secure against such attacks.
GPS jammers are easily available on the Internet. No, we won't link to them. However, truck drivers and others who own company cars often use GPS jammers, and they don't want their employers tracking their every move. Are these devices useful? Is it worth paying $25 for one?
These tiny individual boxes emit radio frequency of about 1575.42 MHz, the same frequency used by GPS satellites in high Earth orbit. These signals from GPS satellites are very, very weak and are relatively easily drowned out by noise. This is pretty much the block diagram for those cheap GPS jammers: Put the noise at the right frequency, and your phone or your boss's GPS tracker won't work. Note that this is a very low-tech attack; In theory, more sophisticated GPS jamming and spoofing techniques could allow drones to land safely.
The dismantling of the GPS jammer shows that the device is very simple. There are some 555s making low frequency noise. This provides the VCO with a signal in the 1466 to 1590 MHz range. The output of the VCO is then sent to a large RF transistor for amplification and output via a quarter-wave antenna. It may be RF magic, but it's a very simple circuit.
The output of this circuit was measured and, to the surprise of many, there were no stray emissions or harmonics - the jammer would not disable your phone or WiFi, only your GPS. The range of the device in the open air is estimated at 15-30 meters, which is more than enough if you're a truck driver. In a canyon of skyscrapers, this range can extend to hundreds of meters.