Quantity   Component name
1 × LED Fiber Optics / Emitters
1 × Coin cell 3V CR2032 Power
1 × Photoresistor GL5516
1 × Resistor 10 kOhm Pull-Up
1 × Resistor 120 Ohm Only for red/yellow/orange LEDs
1 × NPN Transistor 2N4401
1 × Magnet If you want to throw it at metallic surfaces ;)