Its original entrance was on the first floor, reachable only by a retractable ladder, and above that doorway the corbels of a collapsed brick machicolation still protrude from the limestone masonry. Someone later punched a cruder hole through the ground-floor wall to make the building accessible at ground level, which tells you something about the gap between its original military purpose and whatever came after.

The tower was completed by 1805, part of a network of more than eighty signal stations built by the British Board of Ordnance along the Irish coastline in the early years of the nineteenth century. The system was designed to relay warnings of an approaching French invasion fleet, with each station communicating to the next using a naval signal mast. The chain ran clockwise from Dublin Bay all the way to Malin Head in County Donegal, and Mutton Island sat within it: the nearest surviving neighbour in the chain is at Hag's Head, roughly sixteen kilometres to the north-north-east, while the station at Ballard to the south-west, about ten kilometres away, has since been demolished. The threat of French invasion faded by the mid-1810s, and the whole system was quietly abandoned. By the time the Ordnance Survey captured the site in the 1890s it was already being labelled on maps as a ruin.

What survives today is remarkably complete in its fabric, if not its function. The roughly coursed rubble walls retain large sections of original lime render inside and out. Fireplaces at both ground and first floor levels are set into the north-west wall, flanked by alcoves, and the ground-floor surround is cut from limestone of notably fine quality. Bartizans, the small corner turrets that projected from the parapet to allow observation along the outer walls, were originally located at two corners; the corbels supporting one of them still survive even though the turret itself has gone. The rectangular enclosure wall around the tower, slightly misaligned with the building itself, may have been added after the tower was first constructed, and a small ruined outbuilding occupies the western corner of that enclosure. The island also holds the scant remains of St. Senan's Church a little over a kilometre to the east, connecting the site, however loosely, to a much older layer of Clare's history.