The widely publicised telephone conversation allegedly between Princess
Diana and an admirer has alerted the general public to the risks of saying
anything private, personal or secret on any phone which relies on a radio
link. It may also prompt the police and government to use existing laws
to protect privacy.
Cellular phones are inherently insecure, as are most cordless phones
that are used around the home and garden. For less than £200, anyone
can buy scanners which allow them to listen to and record conversations.
Eavesdropping on radio phone calls has now become a hobby.
None of the companies or government bodies involved – British Telecom
(owner of Cellnet), Vodafone, Oftel, Scotland Yard, the Department of Trade
and Industry, and Home Office – has taken responsibility for the problem.
They argue that users of radio phones should always be aware of the lack
Both Cellnet and Vodafone now acknowledge that it is possible to eavesdrop
on calls. ‘It is not illegal to buy or sell the equipment,’ says Cellnet,
‘and the law on use is unclear.’
Under the Telecommunications Act, the Wireless Telegraphy Act and the
Interception of Communications Act, electronic eavesdroppers can be jailed
for up to two years. But the acts have seldom been used to curb such eavesdropping.
The papers which have published transcripts of the ‘Diana’ tapes, and made
them available by telephone to inquisitive readers, have now pushed the
law to new limits.
Telephone calls can be kept secret by using scramblers, but the devices
cost several hundred pounds each and both the caller and receiver of the
call must have one. Converting speech into digital code provides more security,
but so far the digital CT2 cordless phones have been more expensive than
the analogue CT1 phones and have not sold well. Digital cellphones are bigger
and cost more than analogue phones.
Britain’s two cellular phone networks, Cellnet and Vodafone, work with
analogue, frequency modulated speech signals at UHF frequencies of around
900 megahertz. As cell phones became popular, electronics companies started
to sell scanners which could receive these high frequency signals and automatically
scanned a waveband looking for any strong signal.
The cellular network companies have played down the risk of eavesdropping
with scanners, arguing that the two halves of a cellphone conversation,
to and from the mobile phone, are carried on different radio frequencies.
Also, these frequencies change as the caller moves between cells served
by different transmitters.
In 1989 there was a spate of newspaper articles on eavesdropping, revealing
what equipment is needed and how much it costs. An eavesdropper with a single-frequency
receiver can hear both halves of a conversation because the cellphone call
passes through the public telephone network, which mixes both halves of
a conversation so that both callers, on a conventional or a cellular phone,
can hear in their earpiece what they say into their mouthpiece.
The radio cells in an urban area may be only a few kilometres wide,
so the frequency of a moving cellphone will switch every few minutes. Cells
in rural areas are much larger because they need to cater for fewer simultaneous
calls. So when a scanner in the country locks onto a conversation it will
hold it for much longer.
CT1 cordless phones for use at home are even less secure. They use
frequencies just off the bottom end of the medium waveband. Many ordinary
radios will tune to a little outside the marked band and be able to pick
up the signals.