US Patent 9576458 Aspirating smoke detectors

Improvements in and Relating to Aspirating Smoke Detectors Disclosed is an aspirating smoke detection system comprising: at least two different types of detector; and a processor operable to receive signals from the at least two different types of detector, and to determine an alarm status, wherein the alarm status is one of: an all clear status; a critical status; and a status intermediate between the all clear status and the critical status.