Alarm mechanism in a circular gilded and lacquered brass case, with an enamel setting dial (I – XII) in the aperture of the lid. The mechanism consists of a four-wheel train (including fly), mounted between circular plates. On the pillar-plate and on the back of the case is stamped, '515'.

The alarm is contained in an outer cardboard box, covered in green imitation leather. It is inscribed between the Royal Coat of Arms, on an applied oval metal plaque, 'W. GOSSAGE / PATENT'. Inside the box lid is a printed paper label with directions for setting the mechanism.

This device was used in conjunction with a key-wound pocket watch whereby the watch would keep time and would trigger the alarm mechanism at the appropriate moment to sound an alarm.