There's a guy I've bought from on Etsy (I got his SlinkTenna) who makes tiny keychain transmitters, complete with a little straight-key-esque button for tapping out code. It's basically an oscillator chip with some added parts to make it stable. It's ONLY the transmitter, be clear on that. You'll need a receiver to go along with it so you can hear any replies. Here's the link to the 20m model -- if you look on his general page, you'll see he has them on most bands, and the SlinkTenna I bought from him.