Abstract: An electromagnetic warning instrument has a housing equipped with at least one core carrying an operating electric coil, and a contact-breaker cooperating with a vibrating armature fast with a diaphragm. The coil is mounted on a printed circuit and electrically connected thereto. The printed circuit is mechanically fixed to the housing. The contact-breaker is mounted on the circuit by a mechanical connection which effects an electric connection. The printed circuit carrying the coil or coils can be assembled in advance, preferably by automatic means, then it is fixed on the housing, each coil being simply fitted on to the core. The fixing of the contact-breaker assembly then simultaneously ensures a supplementary mechanical connection for the printed circuit and the electric connection with the contact breaker.

Abstract: An alarm system includes a number of self powered indicating elements each with an integral warning device. Each indicating element includes a control circuit which may comprise a transistor switching circuit, transistor oscillator or part of a wheatstone bridge circuit for example. Each of these control circuits is connected via two lines to a common control element at a position remote from the remainder of the control circuit, such element comprising for example a resistor, a battery or a zener diode dependent on the type of control circuit utilized. A switch is also included to provide, on actuation, either a short circuit or open circuit condition between the two lines. Actuation of this switch or tampering with the lines so as to cause a short circuit or open circuit condition to occur will result in operation of the alarm.

Abstract: An electromagnetic acoustic alarm device including a casing formed in part by a bell-shaped wall which defines together with a membrane secured to the casing by means of the bell-shaped wall a chamber, the front portion of the wall provided with at least one opening and a rotatable external plate of the same configuration as the wall front portion having at least one opening for registration to a selected extent with the wall opening so as to adjustably attenuate the high frequency sound component of the device.