This circuit has no lock, but it has a very low consumption feature in the standby condition. We found this alarm in an American publication from the 90s. More sensors can be added. The transistor can be the BD135.

This circuit has no lock, but it has a very low consumption feature in the standby condition. We found this alarm in an American publication from the 90s. More sensors can be added. The transistor can be the BD135.