Dennis Head Old Beacon is a ruined lighthouse on the island of North Ronaldsay, Orkney, Scotland.

It was to be the first of many island lighthouses for Smith (he had previously worked on the lights at Kinnaird Head and Mull of Kintyre).

Its lighting system, although advanced for its time, consisting of a cluster of oil-burning lamps and reflectors was not very effective, often being mistaken for the mast-head of another ship by mariners.

In 1809, with the construction of other nearby lighthouses, it was decided that the North Ronaldsay light was no longer required, and it was extinguished.

The round stone tower was retained as a sea-mark, however, and the original beacon chamber at the top replaced by a vaulted roof, capped by a remarkable ball finial.