12-15V short beep sound simple circuit?
Building on soosai steven's answer, if you use a DPDT relay, you only need one capacitor:







simulate this circuit &ndash; Schematic created using CircuitLab

When the relay pulls in, the capacitor charges through the buzzer. When the relay drops out, the capacitor discharges through the buzzer again. The diode prevents the capacitor from partially discharging through the relay (and any other loads) before the relay drops out.