The flashing is thanks to LEDs with a built-in, integrated flashing circuit and the nasty noise comes from a piezoelectric buzzer — both are available from electronics stores that sell ordinary LEDs.

The two resistors have the same current through them. The potential difference across them will be different if they have different resistances. The total resistance (\(R_{T}\)) for this circuit is ...

For example, often lawnmowers have two switches in series with each other so that both switches need to be pressed before the mower will turn on. The power ring circuit is also a parallel circuit. In ...