The original entrance, set at first-floor level in the south wall and once reached only by a retractable ladder, is protected overhead by a machicolation on three tapering corbels, a defensive slot through which unwanted visitors could, in theory, be discouraged. It is an oddly fortress-like arrangement for what was, at its core, a watchtower for scanning the horizon.

The tower was completed by 1805, one of more than eighty signal stations built by the British Board of Ordnance along the Irish coastline to give early warning of a French invasion fleet. The stations formed a continuous chain from Dublin Bay clockwise around the entire coast to Malin Head, with signalling carried out using naval signal posts. This station on Brow Head sat between the station at Knock, roughly twelve and a half kilometres to the east-northeast, and the one at Mizen Head, only three and three-quarter kilometres to the west, the shortest gap between any two adjacent stations on the whole Irish chain. The threat that prompted the network's construction faded by the mid-1810s, and the system was abandoned. The site did not go quiet for long, however. By the mid-to-late nineteenth century, coastguard buildings and a flagstaff had been added to the southwest of the tower, and a small watch house to the southeast. Then, in 1901, Guglielmo Marconi established an experimental wireless transmitter here, using Brow Head to communicate across the Atlantic with a transmitter at Poldhu in Cornwall. A new building and antenna mount were constructed on site. By 1917, the facilities included a Lloyd's signal station operating flags and lamps alongside a General Post Office radiotelegraph. The tower built to spot Napoleonic warships had become a node in the early wireless network. All the later buildings are now ruined.

The tower sits about 205 metres from the nearest point of the coastline, on gently sloping ground that runs down to Barley Cove to the northwest. A bare rectangular patch at the base of the north wall, where the weather-slating is absent, hints at some abutting structure that was removed at an unknown point; what it was has not been established. The windows, too, carry unanswered questions: their arrangement differs from that found at most comparable towers, and while later alterations around 1900 account for some changes, the weather-slating pattern suggests at least some of the differences may date from much earlier.