In the past, clappers were towers on an elevated site, which were used to summon miners to work shifts. A simple wooden board used to be placed in the upper part of the tower, which was hit (knocked) with a wooden hammer. Longitudinal holes were drilled on the board for better sound propagation. Different methods of knocking meant different warnings and signals for miners and citizens of mining areas. Clappers announced the start of work, but also mining accidents, fire, the approaching enemy army, a meeting, celebrations or the funeral of a miner. To date, probably only 7 clappers have been preserved in Slovakia (Banská Štiavnica, Hodruša, Špania Dolina, Kremnica, Prešov – Solivar, Hnilčík, Liptovský Hrádok).