The structure sits on a natural spur above Balscadden Bay, east of Howth village off Abbey Street, with the rendered exterior and small square window openings typical of its type. Above the doorway on the south-west side, a machicolation survives, a projecting opening through which defenders could drop stones or pour materials on anyone attempting to force the entrance, a detail that speaks to the original military purpose even as the building has long since moved on to other things.

The tower is one of twelve built north of Dublin as part of a coastal defence network constructed from 1804 under the supervision of Colonel Benjamin Fisher of the Royal Engineers. By December 1805, all the Dublin-area towers were armed and complete. Each of the twelve mounted a single 24-pounder cannon, with the sole exception of the tower on Ireland's Eye, which carried two; and unlike some Martello towers elsewhere, none of these northern Dublin examples were accompanied by separate artillery batteries. Martello towers were a standardised British military design of the period, low-profile and thick-walled, intended to resist naval bombardment and deter any Napoleonic landing along the coast. The Howth tower's military career was relatively brief in purely defensive terms. By 1825, the Preventive Water Guard, the revenue service charged with suppressing smuggling, had been granted the right to occupy it as part of their network of coastal stations. It also served as a signalling station and, following the nationalisation of the telegraph companies in 1870, was occupied by HM Postmaster General, giving the old cannon platform an unexpected role in Victorian communications infrastructure. A chimney inserted into the north side is a quiet reminder of these later, more domestic occupancies.

The tower is accessible from Howth village, reached off Abbey Street on the eastern side of the peninsula. From its position on the spur above Balscadden Bay, the tower on the western side of Ireland's Eye is clearly visible roughly a mile and a half to the north, just as it would have been to the garrison watching for signals in either direction. The Hurdy Gurdy Museum of vintage radio now occupies the interior, and the collection inside, radios, wireless sets, and telecommunications equipment spanning much of the twentieth century, makes for an oddly fitting continuation of the building's long association with long-distance communication.