The entrance doorway sits at first-floor level on the south face, originally accessible only by retractable ladder, and is sheltered above by a machicolation, a projecting gallery of rubble stone supported on corbels, through which defenders could theoretically drop things on unwelcome visitors. Brick-built bartizans project from the north-east and north-west corners, each corbelled out from the wall. It is, in other words, a fairly martial-looking little building for something whose main job was to watch the horizon and wave flags.

The tower was completed by 1805 as part of a network of over eighty signal stations built by the British Board of Ordnance in direct response to the threat of a French naval invasion. The system ran as a continuous coastal chain from Dublin Bay clockwise around the entire Irish seaboard to Malin Head in County Donegal, with each station in visual range of the next. Here at Black Ball Head, the nearest neighbours in the chain were the station on Dursey Island, roughly 11.6 kilometres to the west, and another on the west side of Bere Island, about 10.7 kilometres to the east, the latter now largely collapsed. Signalling between stations used a naval signal post, allowing messages to travel the length of the coast in minutes. The whole network was effectively stood down by the mid-1810s once the prospect of a French landing had receded. The enclosure surrounding the tower is irregular in plan, its eastern wall angling away from the usual rectangular layout to work around a natural rock outcrop, a small practical concession to local geology that sets this site apart from the more standardised stations elsewhere in the chain. A small rubble stone outbuilding survives to the north of the tower, and faint cultivation ridges in the surrounding ground speak to the domestic routines of whatever garrison was stationed here during the tower's brief active life.