An aspiration smoke detector (DHA) is a system used in active fire protection. It consists of a system that extracts a small flow of air from the premises to be monitored and conducts it through a network of small diameter pipes (1 to 2 cm) to a central detection unit to detect smoke.[1] The sampling chamber is based on a nephelometer that detects the presence of smoke particles suspended in the air by being able to identify the dispersion they cause in a beam of light. DHAs can generally detect smoke before it is visible to the naked eye.

In most cases, aspirating smoke detectors require a ventilation unit to draw a sample of air from the protected area through its piping network, as is the case with the Wagner, ProSeries Secure Fire Detection and Xtralis DHA systems.[2]​.

In 1970, Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO) used a nephelometer to conduct bushfire research. The Australian Postmaster General's Department subsequently contracted CSIRO to investigate technologies that could prevent service interruption due to fire. CSIRO suggested that the nephelometer should be used as a reference point for APO fire tests. And this type of equipment was installed to monitor smoke levels within the air return ducts of the mechanical ventilation system, using a chart recorder output display.[3]​.

After several weeks of testing, it was discovered that there was no commercially available fire detection technology suitable for preventing damage to telephone equipment. However, a very promising technology was the nephelometer itself.[4]​.

In 1979, Xtralis, then IEI Pty Ltd., produced and sold an air sampling device they called VESDA (Very Early Smoke Detection Apparatus). The company redesigned the detector in 1982 to provide reliability, size and reduced cost to penetrate export markets. DHA systems have gained popularity due to their ability to detect smoke long before an incident turns into a catastrophe.[5]​.

The DHA design corrects the deficiencies of conventional smoke detectors by using a multi-hole sampling pipe. Air samples are captured and filtered, removing any contaminants or dust to avoid false alarms, and then processed by a highly sensitive centralized laser detection unit. If smoke is detected, the system alarm is activated and signals are processed through centralized monitoring stations within a few seconds.[6]​.