FLARM is an affordable collision-warning system for general aviation and recreational flying. It is the only prevalent alternative to the commercial airliners’ expensive ACAS/TCAS system.

See http://www.flarm.com/

I have FLARM installed in my glider GJS and have helped install it on many private gliders and the entire fleet of the GCV. I don't recommend flying without one !

The FLARM is ideal for gliding situations. One of the highest risks we have is traveling in a group. No matter how good our look out (see and avoid) is, we have double blind situations and distractions which are hard to avoid. FLARM helps.

TODO - Aerial discussion and how to check your signal strength (upload file etc)

Get one !

I recommend also looking at: http://www.flarmnet.org/