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A jazz musician named Teri Pall invented a version of the cordless phone in 1965 but could not market her invention, as its 2-mile (3.2 km) range caused its radio signals to interfere with aircraft communications. In 1968, she sold her rights to the cordless phone to a manufacturer who modified it for practical use.
However, cordless phones were still quite expensive, about $400. In 1994, digital cordless phones in the 900 MHz frequency range were introduced. Digital signals allowed the phones to be more secure and decreased eavesdropping -- it was pretty easy to eavesdrop on analog cordless phone conversations. In 1995, digital spread spectrum (DSS) was introduced for cordless phones.