What these products claim
Sellers of stickers, patches, chips and specialty phone cases have long claimed their products block a large share of a phone's electromagnetic emissions, sometimes citing figures like “up to 99%,” often aimed at the area near the earpiece or camera. The pitch is usually a small adhesive patch or a case insert.
What US regulators found when they tested the claims
In 2002, the FTC filed complaints against two sellers of cellphone radiation-protection patches — SafeTShield/NoDanger and WaveShield — for making unsubstantiated claims. Independent testing commissioned by the Good Housekeeping Institute found the patches did not reduce radiation exposure. Both companies settled with the FTC in 2003, and the FTC issued a further consumer warning about similar products in 2011.
Why a small patch can't do what's claimed
The FTC's original complaint identified the core physical problem: most of a phone's RF emission comes from its antenna, which in modern phones is often distributed across multiple points on the device, not concentrated behind the earpiece where a sticker is placed. A patch covering one spot doesn't block emissions from elsewhere on the phone — and any add-on effective enough to meaningfully attenuate the signal would also degrade reception, which can make a phone transmit at higher power to compensate.
What actually reduces exposure
Every phone sold in the US is already tested and certified against FCC SAR limits before it can be sold, so a certified phone complies without an accessory. If you want to reduce your own exposure further, the physics that reliably works is straightforward: increase distance from the antenna (speakerphone, a wired headset, or texting instead of holding the phone to your head), and avoid prolonged calls in low-signal areas, where a phone automatically transmits at higher power to maintain the connection.