Japan Economic Newswire Via Acquire Media NewsEdge) NAGOYA, Aug. 16 -- (Kyodo) _ The Internal Affairs and Communications Ministry has warned the U.S. forces in Japan over unauthorized radio waves emitted by baby monitors used in the homes of military personnel, as they are disrupting radio transmissions nearby for taxi and trucking services, according to ministry officials.

Some foreign-made baby monitors, often used by families of U.S. military and civilian personnel stationed in Japan, emit radio waves stronger than the stipulated level or of similar frequency as mobile phone and radio contact base stations close by, resulting in communication interference in violation of the radio law.

A public relations officer of the U.S. forces in Japan said they are striving to curb illegal radio transmissions and discouraging the use of baby monitors bought in the United States through broadcasting and newspapers for military personnel.

A baby monitor uses a radio system to allow people to check on infants at a distance, such as in separate rooms in a house, by setting a transmitter equipped with a microphone and sometimes a camera near the baby and listening to them or watching them on portable receivers.

Since 2008, there have been increasing cases of detection of illegal radio waves from U.S. military-related residential areas in Okinawa Prefecture, which hosts the bulk of U.S. military bases and facilities in Japan.

The communications ministry's local telecommunications office investigated the cases and determined that the radio waves were emitted by foreign-made baby monitors, according to the officials.

Similar cases have also been reported at residences of U.S. military personnel in Tokyo, Kanagawa, Yamaguchi and Nagasaki prefectures.

As emissions of illegal radio waves continue sporadically in various areas, a ministry official said, "There are also situations in which they could affect important radio communication such as among firefighters. We hope people will not use products that do not comply with Japan's standards." The problem is not unique to U.S. military-related families in Japan, however, as there have also been cases of Japanese people using foreign-made baby monitors and other devices such as transceivers that do not meet Japanese technical standards, leading experts to caution against the use of such foreign-made products.

For example, a Japanese family in Toyama city was found to have disrupted mobile phone communications in September 2009 using a baby monitor purchased in the United States, while in April this year in Nagoya, a Chinese-made baby monitor caused interference in radio communications by trucks.