Personal transponders

[Zedman]

I just did my first race today and despite the SNOW!! it was great fun, I had warm coat and a hat and 4WD so the weather wasn't an issue, what was a pain in the arse was returning the club transponder after ever heat from my muddy wet car and rushing to marshal the next heat, which personal transponder do I buy and where is the best place to buy it from please ?