question about sensors

Are there weather sensors small enough to fly on remote control helicopters and planes and transmit information? If so, where can I find more information about these?
I'd reccommend the Kestrel line of products. Data return is limited, but effective, and they are about the size of an average TV remote.

I got 8 for 800 on ebay. That's $100 each compared to $279 each from kestrel direct. They all worked great, too.