Germany's Bundesnetzagentur, the country's Federal Network Agency, has banned the sale of children's watches that have "eavesdropping" functions.
The agency said that the watches, aimed at children between the ages of five and 12, contained a SIM card and a "limited telephony function" that could be set up and controlled using an app.
The listening function, it said, was often described as a "monitor". App users are able to make the watch call a number without its wearer, or those nearby, noticing.
"Parents can use these children's watches to listen in to the child's surroundings without detection via an app," Jochen Homann, the Bundesnetzagentur's president, said in a statement at the end of last week.
"The watches are regarded as unauthorized transmitting equipment," Homann said. "Our investigations found, for example, that parents were using them to eavesdrop on teachers in lessons."
The Bundesnetzagentur said it was advising schools to increase their awareness of children owning watches with listening functions. If it became aware of people owning the devices, they would be told to destroy them and send proof of this to authorities.
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