A lot of smoke alarm can work toether in a system,, it emits the high frequency digital signal (433.92MHz), the others receive the same signal and will alarm together to remind users to take measures.

Specifications:
1) Power source: One 9V battery, three 1.5VAA
2) Quiescent current: 80uA
3) Temperature: -10º C ~ +40º C
4) Frequency: 433.92MHz
5) Alarm decibel: ≥85dB/3m
6) Size: (diameter) 128x 50mm.