"On the street, cellphone dead zones are annoying; at home, they’re unacceptable. If your calls end every time you cross the dining room, you need a cellular amplifier kit. These little DC-powered devices extend service from the outdoors inside by taking even a faint signal from the closest tower and sending it around your home through an indoor antenna. You can even put an amp in your car to keep a consistent signal while on the road. Besides fewer dropped calls, you’ll also get better battery life, since your phone’s radio won’t be working as hard. The kits are coming down in price, but they still aren’t cheap, so make sure you choose the right one for your situation and set it up correctly. Once you do, you’ll never have to shout “Hello?” again.
How to Tell if Your Amp is Working
Most cellphones have what technicians call “field test mode,” which displays the signal strength more precisely, as negative numbers instead of bars; closer to zero means a stronger signal (zero means you’re standing on a cell tower). Accessing that mode usually requires entering a code. Download this list of codes (PDF) to find the correct one for your phone."