What remains is a spread of rubble no more than about 1.5 metres high, the lower courses of what was once a square-plan structure roughly 4.25 metres across its interior. Amongst the collapsed masonry, one detail survives in recognisable form: an intact rounded bartizan, a small projecting turret of the kind once used for observation or defence, sitting with its conical base amid the debris at the west corner of the ruin. It is a curiously complete fragment within an otherwise comprehensively collapsed building.

The tower at Barr Thráú was one of more than eighty signal stations constructed by the British Board of Ordnance during the first decade of the nineteenth century, all built in response to the genuine threat of a French naval invasion of Ireland. Signalling between stations was carried out using a naval signal post, a system of flags and semaphore capable of relaying information rapidly along the coast. The chain ran clockwise from Dublin Bay all the way around the Irish coastline to Malin Head in County Donegal, with each station positioned to maintain a line of sight to its neighbours. On a clear day, the largely upstanding tower at Tarmon Hill, some twenty kilometres to the south-west at the far corner of the Belmullet Peninsula, is still visible from this site. The station at Benwee Head, around eleven kilometres to the north-east, has fared even worse than Barr Thráú and is now too ruined to be seen from here at all. The whole network was abandoned by the mid-1810s once the threat from France had receded.

The enclosure surrounding the tower repays close attention. A rectangular walled compound roughly 55 metres by 29 metres once defined the station's footprint, and sections of its rubble wall still stand to around 1.5 metres on the north-west side. A shallow external ditch runs along the north-east edge. In the west corner of the enclosure, the grassed-over foundations of a two-roomed rectangular building, probably a store associated with the garrison, remain legible. Perhaps most intriguing is a slight oval hollow about eleven metres north-west of the tower, filled in and marked by a cluster of large stones at its centre. It may be the remains of a lime kiln, used to produce mortar during construction, or it may be the infilled socket that once held the signal mast itself.