The West coast of Guernsey was known for its treacherous reefs. By the early 19th century the increasing number of shipwrecks made it clear that there was an urgent need for a navigation light on this rocky coast. Representations were first made to Trinity House in 1816, but it was over 40 years before a lighthouse was built on the rock known as Le Biseau, part of Les Hanois reef, one mile north west of Pleinmont Point.

The first cargo of Cornish stone arrived in the island in early 1860. The stone was dressed by Cornish craftsmen at the Castle Cornet emplacement to a new design by James Douglass. This involved shaping each stone to a dovetail with its neighbour laterally and vertically, this was the first of it's kind which became standard for all British built sea towers.

Each stone weighed 3-4 tons and was taken to the rock by barge. Gangs of 14-16 men worked on the rock in 14 day shifts. Work often had to be stopped because of high seas; on one occasion five men were swept off the rock and almost drowned. The men were accommodated in Fort Grey. During bad weather they built the Trinity House cottages at Pleinmont.

The lighthouse stands one hundred feet high with a diameter of thirty two feet. The first official lighting was on 8th December 1862; a red revolving light, powered by an incandescent oil burner, producing a bright flash every 45 seconds.

The present light is generated by an electric powered 10000 watt lamp, surrounded by a rotating optic, which gives a light range of 23 miles. The light is white and flashes twice every five seconds. In 1995 the Hanois was converted from diesel to fully automatic solar power. Prior to this, two 3-man crews each worked a 28 day shift on the light.