Digital security codes
One of the first measures made possible by the invention of digital technology was security coding. Every time a handset with this feature is placed into a base unit, one of up to 100,000 digital codes is randomly assigned. This code is then continually transmitted during calls. In order to communicate, a handset and a base unit must have this code.
Digital security codes do not prevent scanners from picking up your calls. The codes merely prevent eavesdropping by other people with similar handsets and make it impossible for them to use your phone line to make their own calls.
Spread Spectrum Technology (SST)
Since binary code is being transmitted (as opposed to analog pulses), digital signals make call interception more difficult. However, eavesdropping is still possible. To further protect cordless privacy, spread spectrum technology was invented. SST disassembles a voice signal, "spreads" it over several channels during transmission, and then reassembles it back into its original form. It is almost impossible for people to reassemble an SST signal on their own. And in addition to better security, since the FCC permits SST phones to use higher output wattage than traditional cordless phones, SST phones deliver better range.
Higher frequencies
Most inexpensive radio scanners—the ones you typically find in electronics stores and/or your local discount drugstore—cannot access frequencies above 512 MHz. However, if eavesdroppers are willing to spend a little more money, they can listen in on a 900 MHz frequency, and beyond.
On the other hand, even the pricier scanners can't cover the 2.4 GHz frequencies used by the newest, most advanced cordless phones.
http://www.marcusball.com/opinion/telecom/...ss_security.htm