A German regulator has banned domestic sales of children’s smartwatches that have a listening function — warning that parents have been using the devices to secretly eavesdrop on teachers at their kids’ school.

In an announcement on Friday, the Federal Network Agency telecoms watchdog said it had already taken action against some online sellers. The target group for the smartwatches are children between the ages of 5 and 12 years.

“Via an app, parents can use such children’s watches to listen unnoticed to the child’s environment and they are to be regarded as an unauthorized transmitting system,” said Jochen Homann, president of the Federal Network Agency in a statement. “According to our research, parents’ watches are also used to listen to teachers in the classroom.”

Back in February, the same federal agency banned sales of an Internet connected doll — called My Friend Cayla — in the country where it’s illegal to manufacture, sell or possess surveillance devices disguised as another object.

On Friday the agency warned there are a large number of providers in the German market that are offering smartwatches for children which contain a listening function, often referred to as a “baby monitor” or “monitor function” in the companion app.

The app owner is able to silently call the device via such functions and listen unnoticed to the conversations of the watch wearer and others in their vicinity — an act of covert surveillance that is illegal in Germany.

The agency has instructed parents to destroy any devices they have bought, and asked schools to be on the look out for smartwatches being used by children — and to request destruction of listening devices they identify.

The Federal Network Agency is not the only European body concerned about risks posed by children’s connected toys, nor specifically by kids smartwatches. Last month the Norwegian Consumer Council put out a report about children’s smartwatches, raising concerns about security flaws, privacy concerns, and risks posed by what they described as unreliable features.

While this month a UK consumer rights group also raised concerns about poorly secured IoT toys which it said could enable strangers to talk to children. The group also called for devices with known security flaws to be banned from sale.

The latest ban may increase pressure for the European Commission to consider whether European Union-wide regulation is needed for Internet connected toys. Back in February, the commissioner for justice, consumers and gender equality, expressed concern, telling the BBC: “I’m worried about the impact of connected dolls on children’s privacy and safety.”