The toy aircraft flew over the prison fence - which is topped with barbed wire - but was soon spotted by a guard when it landed in a patch of open space inside the prison.
It was handed over to bomb disposal experts, who found five mobile phones inside a cardboard box strapped to the aircraft, the daily Kathimerini newspaper reports.
Along with the phones were five charging cables, six SIM cards and two sets of headphones, the Greek news agency AMNA reports.
But even though the prison's security was alerted immediately, guards didn't find anybody in the surrounding area and continue to search for the person who was controlling the helicopter.
Source: Kathimerini
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