A Bullet-probe was a Cardassian surveillance device and weapon used in the 24th century. They featured a duranium sheathing and would activate and scan energy signatures as they detected them, they then functioned as a mine to try and destroy the target.
The Cardassians commonly used bullet-probes in the Bajoran system, when it was under the Occupation, to try and detect Bajoran Resistance fighters. In 2370 at least one bullet-probe was used in the Davon system to guard the Cardassian mining moon Davonia. (DS9 novel: Devil in the Sky)