There's a company in Switzerland manufactures an anticollision system for
gliders called FLARM. A gadget in your glider continuously broadcasts your
GPS position over a low power radio. Gadgets in other gliders so-equipped
receive the position messages and using an appropriate algorithm to
determine if there is any risk of collision. If there is such a risk, a
warning sounds and a position indicator shows the sector of the risk.

I think the algorithm can track multiple gliders and is smart enough to
determine if you are all in the same thermal and so keeps quiet.

The website is www.flarm.com.

Has anyone out there got any experience of this system and does anyone know
if there are alternative self contained systems available (i.e. that don't
rely on transponder responses, for example)?