The phones, which are no larger than lighters, have been marketed as impossible to detect in security checks. Approximately 5,000 mobiles are estimated to be in circulation.
In total, 500 cells at 66 different prisons in the country will be searched in the hunt for mini-mobiles, manufactured in China but sold on by a French reseller. The operation goes under the name "Prison break".
Some of these phones have been used to commit crimes such as drug trafficking, fraud, arson attacks on companies, and attempted murder from within prisons, says Paris prosecutor Laure Beccuau.
The French reseller has had its website blocked in the country.
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