Abstract: A fire detection system of the type utilizing an optical detector with discriminating photo-cells connected in series to form a voltage divider, with the rise in voltage at the junction of the photo-cells being utilized as the input to an amplifier to energize an alarm or actuate an extinguishing system, in which the ground wire to the remote optical detectors is also used as the ground wire between the amplifier and the actuating means for the alarm or the extinguishing system, whereby a break in the ground wire, which causes a rise in voltage at the junction, is prevented from causing a false alarm, since said break also breaks the circuit between the amplifier and the actuating means.

Abstract: A portable fire alarm device comprising fire detecting means and alarm means powered from a self-contained power supply. The power to the detector and alarm is through a normally closed switch of the type such as a mercury switch which may be opened by tilting the device to a predetermined angle from the vertical so that the alarm may be shut off.A second normally open switch of the mercury type connects the power supply directly to the alarm device and is so oriented that tilting the device to a predetermined angle from the vertical closes said switch and energizes the alarm to test the condition of the battery.