Step 3: Reed Switch
The reed switch is comprised of two pieces, a switch and a magnet. The switch has two wires extending out from it, when a magnet comes near the switch it causes a small mechanical piece to move and close the switch momentarily.
Solder a 10kOhm (current limiting) resistor between A0 and ground on the protoboard. Connect long pieces of stranded wire to A0 and 5V- these wires will wrap around the bike and attach to the reed switch.