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Object Overview
This Alarm Barometer, produced around 1970 by the British company Bevan Seatech Ltd., is an aneroid barometer with an integrated warning system for dangerous drops in atmospheric pressure. The construction combines a mechanical pressure sensor (a sensitive aneroid capsule with a U-shaped spring) and a magnetic contact adjusted to a specific pressure threshold. When the pressure falls to the preset level, the contact closes and activates an acoustic alarm (buzzer). In this way, the instrument automatically warns of a sudden deterioration in weather conditions — an approaching storm or gale.
The barometer is housed in a small rectangular case of mahogany, finished with a transparent lacquer that brings out a deep, warm gloss. The American mahogany is hand-polished, with rounded edges and a neat recess cut for the adjustment wheel on the lower edge. On the back of the case, a central brass screw secures the entire mechanism; once loosened, the complete inner assembly, together with the front panel, can easily be removed — for example, to replace the battery.
121
aneroid capsule tensioned on a C-spring
beryllium, brass, plastic, steel, wood
The front panel is made of plexiglass laid over a plastic base painted in a golden tone. All inscriptions — from scale units to the company name — are engraved into this plastic base. At the center of the panel are two openings covered with golden mesh, allowing the alarm signal to be heard clearly.
The dial consists of a straight paper scale graduated in millibars from 950 to 1050. The dial is used exclusively to set the threshold value at which the alarm will sound, by sliding along the scale a red marker; this is adjusted using a knurled wheel recessed into the lower part of the case, which requires the barometer to be tilted or lifted for access.
The instrument has no external display or pointer for the current atmospheric pressure. It was designed solely as an alarm barometer — a device that automatically alerts the user when the pressure drops sharply. This was particularly useful in the maritime context (yachts, fishing vessels, coastal stations), where a rapid fall in pressure forecasts storms or cyclones.
Despite its austere exterior, the barometer conceals a combined aneroid–electrical mechanism based on the principle described in U.S. Patent No. 3,623,051 (Juno & Pruitt, 1971).
At its core is a classical aneroid capsule made of beryllium bronze — a sealed metal capsule sensitive to changes in atmospheric pressure. As the pressure falls, the capsule expands, acting against the restraining U-shaped spring and in turn moving a lever with a small magnet at its end. This magnet approaches a reed switch (a magnetically responsive contact) mounted on a brass plate and wired to a simple electronic buzzer powered by a battery.
Construction details:
The entire system is powered autonomously by a single AA cell housed inside.
The Baralarm by Bevan Seatech Ltd. is a striking example of how late 20th-century engineering combined the mechanical reliability of the aneroid capsule with the new capabilities offered by simple electronics. It stands at the intersection of marine navigation, meteorology, and industrial design, and may be regarded as a precursor of modern electronic weather stations with automatic alarms.
Instruments of this series were produced only in limited numbers — the present example, bearing serial number 121, belongs to the early stage of production. Over time, Bevan Seatech devices have become rare, today attracting the interest of both collectors and historians of technology.