Sonic cone

A sonic cone was a device used for defending an area. Anything that breached a designated perimeter around the cone was atomised.

Gavrok deployed a sonic cone atop the Seventh Doctor's TARDIS. Hawk breached the perimeter and his hand was burnt. Gavrok fell into the perimeter whilst in disarray and was atomised. With the power drained the Doctor merely removed it. (TV: Delta and the Bannermen)