Cell phone signal boosters claim to increase the signal strength of your cell phone connections giving you clear calls that are less likely to be dropped. Given the unpredictable nature of cell phone signals with the signal often varying even if you move a few feet from where you stand now; it is really hard to determine if these boosters actually work.
The most popular version of cell phone boosters I've seen are small stickers that appear to have circuitry within the sticker. This circuitry may be described as an extended antenna that allows the phone to capture more from nearby cell towers. I actually had the chance to try one of these stickers a few years back and I'm not sure I can say it did anything but leave residue on my phone when I tried to remove it; but my experience aside lets look a bit deeper into the concept behind cell phone boosters.
Cell phones are constantly sending and receiving information to cell phone towers; your phone's signal strength varies based on the strength of the connection between phone and tower. Conditions such as weather, metal materials, and distance from towers can affect the signal strength. Weakened signals lead to poor call quality, slower connections, and more dropped calls. Cell phone signal boosters seem to assume that a larger attune will fix the problem.
I've heard a few kinds of explanations for cell phone boosters and how they work. Some people are under the belief that these stickers somehow turn the whole phone into a conduit through which to receive signals from towers. Being that these stickers have no power supply, I can't see how that is possible. Another reasoning is that somehow the stickers collect the radiation output of a cellphone and redirect that energy into signal strength. Again you don't have to be an electrical engineer to figure out that probably doesn't work or even make sense.
The simplest explanation seems to suggest that the stickers are nothing more then coiled up metal that acts as an extra antenna for your phone. But the application of these sticker boosters wouldn't do much because in order to boost your signal capturing abilities, you'd need some sort of external device to connect to the phone's built in antenna which is wired to the phone. The sticker is generally applied under the phone battery against where the phone's internal antenna is supposed to be. Again the design of the phone doesn't line up with the signal booster sticker's claims. Some phones have external antennas, while others have internal attenuates that can be anywhere in the phone.
People of course do claim these work, after all if no one was buying signal boosters, they would cease to exist. Some people may slap one of these on their phone after spending a few bucks on one and later on make a call and claim that the call was clearer or they had more signal bars on their screen. Of course the constant change of a phone's position in relation to towers, weather conditions, the network's current status, and the quality of the other caller's network all affect the signal quality second to second.
On top of that people may think that the phone call quality is better simply due to the psychological affect. The makers of the boosters claim they work and say you'll notice a difference, so most people put them on and immediately go to make a call and falsely believe the signal improved. Even if the phone shows more signal bars after adding the booster, that again could be due to changes in the phone's position, network conditions, and weather conditions.
Overall there is no conclusive way to prove that these cell phone signal boosters work but common sense and available evidence suggests that there are too many other conditions affecting a cell phone's operating abilities and environment to conclusively say that cell phone signal boosters actually work. Save your money and find a cell phone provider that works well most of the time and offers high quality phones that will work in many places and under many conditions.