FIRE ALARM

PURPOSE: To obtain an inexpensive fire alarm capable of intermittently driving a buzzer at the time of detecting the reduction of battery voltage, and reducing current consumption. CONSTITUTION: The fire alarm is provided with an oscillating and light emitting circuit 1 for intermittently emitting a light emitting element(LEE), a clock signal generator 2 for generating a clock pulse signal synchronously with the intermittent light emitting period of the LEE, a light receiving and amplifying circuit 3 having a light receiving element for receiving scattered light due to the smoke particles of light emitted from the LEE and transducing the received light into an electric signal pulse and allowed to amplify the electric signal pulse and output the amplified pulse, and a fire judging circuit 5 for outputting an alarm signal synchronously with the clock pulse signal when the pulse signal from the circuit 3 is more than a reference value. The fire alarm is also provided with a buzzer driving circuit 6 for receiving the alarm signal from the circuit 5 and outputting an alarm driving signal, an alarm 7 to be driven by the alarm driving signal outputted from the circuit 6 and a voltage drop alarming circuit 8 for detecting the voltage of a battery power supply 13, and when the detection value is less than a prescribed value, outputting an alarm signal to the circuit 6.