Designed to be “leaky”, it permits only a fraction of the RF radiation to penetrate. Exposure to people is reduced (typically 90-99% reduction), and the device usually still works, but with a more limited range. Great for when you permanently or temporarily want to quiet microwave levels without fully turning off the source. Place it over cellphones, cordless phones, two-way radios, smart devices, even wifi routers. Sturdy metal. The two larger units have convenient handle and access holes for wire and cable pass through. Pick the sizes which meet your needs.
If you're looking for ways to limit your exposure to the electromagnetic emissions from your cell phone, know that, according to the FTC, there is no scientific proof that so-called shields significantly reduce exposure from these electromagnetic emissions. In fact, products that block only the earpiece – or another small portion of the phone – are totally ineffective because the entire phone emits electromagnetic waves. What's more, these shields may interfere with the phone's signal, cause it to draw even more power to communicate with the base station, and possibly emit more radiation.
The U.S. government doesn’t seem very troubled, either. The Food and Drug Administration says on its website that research generally doesn’t link cell phones to any health problem. And although the Federal Communications Commission requires manufacturers to include information in user manuals about cell-phone handling, that’s often buried deep in the fine print.
The frequency of radiofrequency electromagnetic radiation ranges from 30 kilohertz (30 kHz, or 30,000 Hz) to 300 gigahertz (300 GHz, or 300 billion Hz). Electromagnetic fields in the radiofrequency range are used for telecommunications applications, including cell phones, televisions, and radio transmissions. The human body absorbs energy from devices that emit radiofrequency electromagnetic radiation. The dose of the absorbed energy is estimated using a measure called the specific absorption rate (SAR), which is expressed in watts per kilogram of body weight.