I found this while surfing Craig's List, a tiny QRP transmitter that fits on your keychain: https://www.etsy.com/shop/QuirkyQRPHamRadios I have no affiliation with the seller. The price is $39.95, the documentation is sparse. Looks like it runs on 9V and puts out 160mW. They recommend an external LPF. Looks like there are models for different bands, the page shows one that's marked 100.0 Mhz, CW on the FM BC band?
