SART stands for Search and Rescue Transponder.
It is a device for locating ships or their survival craft in distress.
The SART operates in the 9 GHz frequency band – generating a series of dots when being interrogated by a search craft with an X – Band (3cm) radar.
As the search craft approaches to within 1 nautical mile of the SART, the 12 dots change to wide arcs and eventually into complete circles as the search craft nears the SART.
For the person in distress the SART provides a visual and acoustic indication when being interrogated.
The detection range from a rescue ship to the SART is a minimum of 5 nautical miles, and from a Search and Rescue helicopter up to 40 nautical miles.