S 5.80 Protection against bugging of indoor conversations using mobile phones

Initiation responsibility: Head of IT Section, IT Security Management

Implementation responsibility: IT Security Management

The only way to be sure that indoor conversations are not being bugged using mobile phones is to prohibit the taking of mobile phones into the rooms to be protected. If the IT security policy of an agency or company does not allow mobile phones to be brought into the building, clear notices to this effect must be placed on all the entrances. But without corresponding checks, a simple notice will generally be ineffectual.

Switching off the mobile phone does not ensure sufficient protection since in the case of manipulation there is no way of eliminating with certainty the possibility of the phone being switched on over the radio link. The only way to prevent this would be to remove the battery.

Mobile phone detectors

Mobile phone detectors are devices which detect whether one or more mobile phones is in transmission mode (i.e. a conversation is taking place) within a defined area.

Passive warning devices are available on the market which report any mobile phones in transmission mode. The range of the devices can be adjusted so that it is confined to the area to be monitored. It is recommended that if this kind of protection is required, warning devices are installed and these are activated when conversations about sensitive or confidential matters are taking place.

However, these passive detectors cannot detect mobile phones which are currently in standby mode. Detection of such mobile phones is only possible if the detector has an active transmitter component. This transmitter component can then require the mobile phone to go into transmission mode. Once the mobile phone is in transmission mode, it can be picked up with a detector.

These active detectors are appropriate for conversations which involve sensitive material. They can detect all mobile phones that are switched on. Any mobile phone switched on subsequently has to register itself with the base station, and this action can be detected also. Another possibility is to use noise pulse generators to interfere with radio operations in a spatially defined area so that reception of mobile radio signals is not possible there.

At present only passive mobile phone detectors can be recommended. While active detectors could also be helpful, their use cannot be recommended in Germany as they are not approved for use in the Federal Republic of Germany. The same applies to transmitters which jam radio operations, which are also illegal in Germany.