Abstract: An enviromental abnormality alarm apparatus includes a plurality of terminals connected to a transmission line and a central processing unit. A specific address is assigned to each of the terminals. The central processing unit sequentially circularly accesses the addresses of the terminals and receives a signal corresponding to a physical change such as a fire, gas leakage, or burglary supplied from each terminal. Each terminal includes an alarm determination reference setting unit, a comparator for comparing the physical change signal with an alarm determination reference value, and an output unit for supplying a comparison result from the comparator. The alarm determination reference value of the alarm determination reference setting unit is set by transmitting and receiving data to and from the central processing unit.

Abstract: In a smoke detector of the type in which smoke is detected in a detection chamber based upon a variation of an ionization current flowing therein or a variation of light beam passing therethrough, there is provided a reference signal generating section which produces a reference signal having a predetermined characteristic corresponding to typical smoke flowing into the detection chamber when a fire occurs, and a signal comparison section which compares a detection signal detected in the detection chamber with the reference signal, wherein a smoke sensing signal is produced when the detection signal is determined as a signal due to a fire but is not produced when the detection signal is determined as the signal due to the entry of an insect into the detection chamber or due to cigarette's smoke flowing thereinto.