A great variety of methods for detecting landmines have been studied. These include electromagnetic methods, one of which (ground penetrating radar) has been employed in tandem with metal detectors. Acoustic methods can sense the cavity created by mine casings.
Safe tiles contain a number signalling how many of the 8 adjacent tiles are armed1. Since revealing tiles next to a 0-tile cannot make the player lose the game, clicking on a 0-tile will make all the adjacent tile to be revealed as well.