A Bluetooth tracker hidden in a postcard allowed for 24-hour tracking of the location of a Dutch warship.

Dutch broadcaster Gelderland Radio reported that they were able to track the location of the Dutch Navy frigate '

Marineschip van 500 miljoen euro gevonden met gadget van 5 euro - Omroep Gelderland
https://www.gld.nl/nieuws/8463135/marineschip-van-500-miljoen-euro-gevonden-met-gadget-van-5-euro

Dutch navy frigate tracked by mailing it a Bluetooth tracker • The Register
https://www.theregister.com/2026/04/17/dutch_navy_frigate_tracked/

Bluetooth tracker hidden in a postcard and mailed to a warship exposed its location — $5 gadget put a $585 million Dutch ship at risk for 24 hours | Tom's Hardware
https://www.tomshardware.com/tech-industry/cyber-security/bluetooth-tracker-hidden-in-a-postcard-and-mailed-to-a-warship-exposed-its-location-a-eur5-gadget-put-a-eur500-million-dutch-ship-at-risk-for-24-hours

The Dutch Ministry of Defence has established its own postal system to allow soldiers to stay in contact with their hometowns, and has published information online on 'how to send mail so that it reaches soldiers.' Gelderland Broadcasting purchased a Bluetooth tracker costing around 1000 yen and sent it to Evaazen by mail to explore potential vulnerabilities.

Of course, the Ministry of Defense checks all mailed packages with X-ray scanners to prevent the transport of prohibited items and dangerous goods. However, it seems that postcards were designed to bypass the X-ray scanners. Gelderland Broadcasting was able to send postcards to Ewartzen by embedding Bluetooth trackers into them, thus avoiding detection of the trackers.

The Bluetooth tracker's route could be tracked online, and according to Gelderland Broadcasting, it traveled from the sorting center, via the naval base in Den Helder, to Eindhoven Airport. It was then transported to the port of Heraklion on Crete, and brought aboard the Ewazen, which was docked there.

Map data from OpenStreetMap

While the Evazen's anchorage in Heraklion harbor was publicly broadcast via the harbor's live cameras, its location after departure was kept top secret for mission reasons. However, thanks to a Bluetooth tracker, Gelderland Radio was able to continue tracking the ship and confirmed that the Evazen sailed west along the coast of Crete before changing course eastward towards Cyprus.

Approximately 24 hours later, when the Ewartzen arrived near Cyprus, its Bluetooth tracker went offline. According to the Ministry of Defense, the tracker was discovered during mail sorting operations after departure. Although the Ewartzen was trackable at sea, it was stated that it did not pose an operational risk.

A review of the postal system is already underway, and it is no longer possible to send postcards containing batteries to Ewartzen. A review of the guidelines for military mail is also planned. Meanwhile, information on how to send mail will continue to be made public.

Former Vice Admiral De Kruyf stated the importance of location information, saying, 'While it's now possible to remotely attack targets with high precision, attacks still require location information of the target. That's why a frigate would never want to reveal its position to others.'

It should be noted that incidents of warship location information being leaked occur frequently, and in March 2026, a French soldier accidentally leaked his location information through a sports app.

The location of a French aircraft carrier was revealed through the fitness app 'Strava' - GIGAZINE