Grave Guns, Cemetery Guns, Trap Guns.

This type of firearm was generally used to protect graves from grave robbers in the 18th century. These grave robbers worked at night so as not to be seen, but this also meant that they may not see these guns mounted on a grave, & would probably not see the trip wires. Several trip wires could be fitted to the trigger mechanism, running in different directions. This not only covered a wide area, but it also meant that any one of these wires could swivel the gun in the direction of the intruder.

http://www.guns.com/2013/08/06/cemetery-guns-and-coffin-torpedoes/;

http://milpas.cc/rifles/ZFiles/Odd%20Fellows/18th-century%20French%20Flintlock%20Grave%20Robber%20Trap%20Gun/18th-century%20French%20Flintlock%20Grave%20Robber%20Trap%20Gun.htm;

http://www.collectorsfirearms.com/flintlock-spring-gun-bp552/;