The roughly six-metre-square structure at Knock, completed by 1805, still has its original first-floor doorway to the south elevation, once accessed only by a retractable ladder, now reached by a flight of concrete steps leading to a modern balcony. The rubble stone machicolation above the door, a projecting parapet feature that would have allowed defenders to observe or drop objects on anyone below, remains in place, though it has been heightened and fitted with glazed screens. Corner bartizans, small projecting turrets supported on corbels, survive at the north-east and north-west corners in similarly altered form. The whole exterior, originally lime rendered with weather-slating, is now cement rendered, and a large modern bungalow has been built adjoining the original structure to the west and north-west. The military architecture underneath is still legible if you know what to look for.

The tower was one of more than eighty signal stations built by the British Board of Ordnance along the Irish coastline in the early nineteenth century, forming a continuous chain from Dublin Bay clockwise around the entire coast to Malin Head in County Donegal. The purpose was straightforward and urgent: to relay warnings of an approaching French invasion fleet using naval signal posts, passing information rapidly from station to station along the chain. The Knock tower, completed by 1805 according to researcher Paul Kerrigan, sat between the station at Brow Head roughly twelve and a half kilometres to the west-south-west and the station on the east side of Clear Island about twelve kilometres to the south-east, both of which survive to their full original height. A battery at Leamcon lay just over a kilometre to the south-south-west. By the mid-1810s, with the Napoleonic threat receding, the entire system had been abandoned. Hamilton's map of 1806 shows the tower sitting within a narrow rectangular enclosure, and the Ordnance Survey maps of the 1840s record both an inner and a larger outer enclosure, along with a small rectangular building to the east of the tower; by the end of the nineteenth century, both the inner enclosure and the outbuilding had disappeared. The garden boundaries of the present dwelling appear to follow broadly the line of the larger outer enclosure as it was recorded in the 1840s.