Alexisgm97 documents this LED keychain project on Instructables:
Today I am going to show you how to make a very cool LED keychain. To do this, we are going to use an ATtiny to make the LEDs blink and fade. This is going to help us to learn how to solder SMD components and also how to program an ATtiny.
You can also find the code here in case you want to modify it or even create a new one! This code has 4 modes: All on, slow blink, fade and fast blink that change every time we press the button and then it enters in sleep mode to save battery.
Once we have finished, we can carry our creation around with our keys as a keychain!
Are you ready? Enjoy!