You’re going to need a white or blue LED that is rated for 3 volts, a 1K resistor, a 2N 3904 NPN transistor, a toroid, two pieces of wire and a battery.
You might even be able to scavenge this stuff out of your junk pile of electronics… you have a junk pile of electronics right? PDF Link
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Update: Windell posted more info and a detailed walk through of the toroid winding process. – Link