I bought one of those little chinese qrp tuners and built it for the practice. It does work better than I expected.

anyhow If you put a dummy load on it and your qrp tranceiver/ transmitter on it while in tune mode (off tuned of course) when you key your straight key or paddle the led will light up If your radio is actually transmitting a signal!

This makes a handy tool for troubleshooting! If your not transmitting when you depress the key then something is wrong! (quick and dirty rf probe)