Your circuit Will Not Work because the LMC555 has a low output high current of not much more than only 10mA. The 39 ohms resistor in series with the base-emitter of the transistor is a short circuit to 10mA. The 555 switches when its pin 6 voltage reaches 2/3rds the 13.2V supply which is 8.8V. But then the output current from the 555 must be at least (8.8V - 1V)/39 ohms= 200mA. An LMC555 cannot do it and an ordinary LM555 or NE555 can barely produce the required 200mA.Here is a much more simple version of a European siren using 555's. Both 555's use the symmetrical astable circuit from the LMC555 datasheet.

Gary, the TDA7241 is not available anymore. Use a similar but more modern TDA7396 car mono amplifier instead.