Dotson said he is concerned about openness and transparency, and said that a password-protected website was being set up to try to keep the news media informed. He also pledged to revisit the issue in a month to measure the effects of the change.

Asked about limiting access by news media, hobbyists and the general public to police information which has traditionally been available, Dotson said he was not comfortable having addresses of crimes and callers overheard by the public.

Across the country, some departments use encryption, some don’t and some encrypt only certain communications. No major agencies have used it in the St. Louis area, although Alton police have for years coded certain messages. It has become more feasible as advancing technology and demand for radio bandwidth have moved police to digital radio systems.

An encrypted message will sound garbled on some scanners, or may not be heard at all on others.

Police in many places, including St. Louis, have eliminated much of their radio traffic anyway by using mobile data terminals to send texts. Some also use Nextel, which as a commercial cellphone and two-way radio service is difficult and illegal to monitor.

Equipment to decode encrypted signals is not sold to the public, and unauthorized use of it is against federal law.

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