A smoke detection system comprising: a particle detector having an ordinary detection mode and a high speed detection mode; the particle detector comprising an aspirator; an air sampling network having: at least one sampling pipe with a plurality of sampling inlets through which smoke can enter the air sampling network; the aspirator being configured to draw air samples through the sampling inlets, along the sampling pipe, to the detector for analysis; a fan and a valve at a distal end to the detector; a mechanism (1522, 1524) for delivering purging air to the air sampling network; and a mechanism for controlling the valve and the fan, the smoke detection system being configured to: operate in a detection mode in which the aspirator draws air through the sampling inlets along the sampling pipe to the particle detector for analysis; operate in the purge mode to purge the air sampling network of particle laden air and displace it with clean air; operate in a localisation mode in which the particle detector operates in a high speed detection mode which smoke detection response is faster than the ordinary detection mode, to determine which of the plurality of sampling inlets smoke has entered the air sampling system, wherein the localisation mode comprises the purge mode. a particle detector having an ordinary detection mode and a high speed detection mode; the particle detector comprising an aspirator; an air sampling network having: at least one sampling pipe with a plurality of sampling inlets through which smoke can enter the air sampling network; the aspirator being configured to draw air samples through the sampling inlets, along the sampling pipe, to the detector for analysis; a fan and a valve at a distal end to the detector; at least one sampling pipe with a plurality of sampling inlets through which smoke can enter the air sampling network; the aspirator being configured to draw air samples through the sampling inlets, along the sampling pipe, to the detector for analysis; a fan and a valve at a distal end to the detector; a mechanism (1522, 1524) for delivering purging air to the air sampling network; and a mechanism for controlling the valve and the fan, the smoke detection system being configured to: operate in a detection mode in which the aspirator draws air through the sampling inlets along the sampling pipe to the particle detector for analysis; operate in the purge mode to purge the air sampling network of particle laden air and displace it with clean air; operate in a localisation mode in which the particle detector operates in a high speed detection mode which smoke detection response is faster than the ordinary detection mode, to determine which of the plurality of sampling inlets smoke has entered the air sampling system, wherein the localisation mode comprises the purge mode. operate in a detection mode in which the aspirator draws air through the sampling inlets along the sampling pipe to the particle detector for analysis; operate in the purge mode to purge the air sampling network of particle laden air and displace it with clean air; operate in a localisation mode in which the particle detector operates in a high speed detection mode which smoke detection response is faster than the ordinary detection mode, to determine which of the plurality of sampling inlets smoke has entered the air sampling system, wherein the localisation mode comprises the purge mode.