of the band led to an allocation of additional frequencies; thus manufacturers were able to sell models with 25 channels instead of just 10 channels. Although less susceptible to interference than previous AM units, these models are no longer in production and are considered obsolete because their frequencies are easily heard on practically any radio scanner. Advanced models began to use voice inversion as a basic form of scrambling to help limit unauthorized eavesdropping. These phones share the 49.8 MHz band (49.830 - 49.890) with some wireless baby monitors. 900 MHz cordless phones are rarely sold but have a huge installed base. Features include even shorter antennas, up to 30 auto selecting channels, and higher resistance to interference. Available in several varieties; analog, analog spread spectrum (100 kHz bandwidth), digital, and digital spread spectrum, most being sold today are low-cost analog models, which are still susceptible to eavesdropping. Digital variants can still be scanned, but are received as a digital hiss and therefore are difficult to eavesdrop upon. Digital transmission is immune to static interference but can experience signal fade (brief silence) as the phone goes out of range of the base. Newer Digital Spread Spectrum (DSS) variants spread their signal over a range of frequencies, providing more resistance to signal fade. This technology enabled the digital information to spread in pieces among several frequencies between the receiver and the base, thereby making it almost impossible to eavesdrop on the cordless conversation. The FCC only allows DSS model phones to transmit at the full power of 1 watt, which allows increased range over older analog and digital models. Virtually all new cordless phones sold in the US use DECT 6.0 on the 1.9 GHz band, though legacy phones can remain in use on the older 900 MHz, 2.4 GHz and 5.8 GHz bands. There is no specific requirement for any particular transmission mode on the older bands, but in practice many legacy phones also have digital features such as DSSS and FHSS. Some cordless phones formerly advertised as 5.8 GHz actually transmit from base to phone on 5.8 GHz and transmit from phone to base on 2.4 GHz or 900 MHz, to conserve battery life. The 1.9 GHz band is used by the DECT 6.0 phone standard and is considered more secure than the other shared frequencies. The vast majority of new cordless phone devices sold in North America, whether