As I was trying out some ideas I had for my next tube audio amplifier build, I came up with an idea for a keychain. I had a few 5727 thyratron tubes in my junk box and I really have no use for them so I decided to sacrifice one to make a little LED powered keychain. I turned a suitable base for the tube out of brass and made a plastic battery holder for a CR1632 lithium button cell. I used a low current orange LED and I was surprised to find out that even without a current limiting resistor the LED continued to glow for a full week straight. I have since put a resistor in series with the LED but I haven't tried how long it will stay lit. The keychain is made of brass and stainless steel. The power switch is a simple spring loaded screw in the bottom of the keychain.